The American men walked into the darkened brothel in Bangkok and were soon offered a variety of prostitutes, young and old, male and female. "You go in and try to look like a john as much as possible," one of the Americans said later of his undercover role. "Try to act like them, talk like them. You don't go in and order a glass of milk."

The men moved from brothel to brothel, each "packed with foreigners," the American said. "You're sitting next to these perverts, not only having to interact with them but become one of them. It's common to go shop around. You sit there, get a price," he said. "It was probably the darkest underworld playground of the devil that I've ever been in."

The American was former Washington Nationals baseball player Adam LaRoche, and he described participating in a "rescue" operation last year with The Exodus Road, one of a number of American nonprofit groups that are fighting human trafficking in a new way: by luring pimps into the open, and then working with local law enforcement to arrest the traffickers and free the victims.

Members of the groups, often former U.S. military members or law enforcement officers, pose as American tourists looking to party with groups of underage sex workers. Some groups, such as The Exodus Road and Operation Underground Railroad, invite supporters or television crews to come along to spread word about the horrors, and witness the thrilling moments when sex traffickers are handcuffed, and terrorized children are rescued.

"We believe the problem will never go away unless everybody knows about it and does something," said Tim Ballard, a former investigator with the Department of Homeland Security who started Operation Underground Railroad, based in Anaheim, California.

But this high-profile approach is attracting skepticism from some respected workers who have fought human trafficking for decades by working with Third World police and prosecutors to attack the problem and rid their ranks of corruption. They question whether the American groups spend the time and effort needed to ensure that victims aren't returned to the same cycles of degrading violence. They also raise concerns about entrapment and safety for the civilians such as LaRoche who participate.

"The trouble is it's really risky to the victims," said Anne Gallagher, founding chair of the U.N. Inter-Agency Group on Human Trafficking and Migrant Smuggling, and cited by the State Department as "the leading global expert on the international law on human trafficking." She said that the civilian groups can cause problems for prosecutions, and that they often are unprepared to help victims.

"It's also misleading," Gallagher said, "and deflects attention and resources and energy away from the hard stuff that needs to be done. . . . They're in and out. No way they can follow up a victim's case. No way they're evaluating the impact of what they've done."

Gallagher and Cees de Rover, executive director of Equity International, wrote an article for the Huffington Post last year criticizing Operation Underground Railroad from "a law enforcement perspective." The group's approach, the pair said, targets low-level recruiters and pimps but doesn't dismantle the leadership of sophisticated trafficking networks.

Gallagher said Americans entranced by the promise of quick rescues "don't want to hear the news that it's a hard slog. You've got to keep doing it for years and years."

But groups such as Operation Underground Rescue and International Justice Mission, often mentioned as the preeminent rescue group, say that they do plan for the care of rescued victims, and that their work is having a measurable effect on human trafficking and sex tourism in countries such as Cambodia, the Dominican Republic, the Philippines and Thailand. The rescue organizations are funded entirely by private donations, government and private grants and in-kind offers of goods and services, their officials said.

Holly Burkhalter, the senior adviser for justice system transformation at the International Justice Mission, based in Washington, said that her group establishes permanent staffs in the countries where they work, and that they create lasting relationships with both social service providers and law enforcement.

"We stay there for the long term," she said. "If children coming out of a criminal sexual situation are not given care and schooling and economic aid, they will almost certainly be retrafficked. We are absolutely involved every step of the way."

The rescue groups work closely with law enforcement in the host country to oversee their rescue missions and handle the prosecutions of the traffickers. Gallagher said that can be problematic in many countries where law enforcement is already deeply involved with the traffickers.

The most widely accepted analysis of human trafficking worldwide, by the International Labour Organization in 2012, estimated that 4.5 million people are being forced to work in the sex trade, out of 20.9 million in all manner of forced labor. The State Department's Trafficking in Persons report for 2016 said there had been nearly 19,000 prosecutions worldwide for human trafficking last year, an 88 percent increase from the previous year.

When American rescue groups offer their help, it's generally appreciated by the United States and host governments, even if it isn't always comprehensive, said Ransom J. Avilla, a Department of Homeland Security Investigations attache based in Manila. Avilla said American officials in the Philippines had worked closely with the International Justice Mission and "they do provide a full service," working with police, prosecutors and social service agencies throughout cases that can last many years.

He said that it is possible that child victims sometimes fall through the cracks, but that, in general, "I think any group that wants to be here combating these cases is helping the country."

Ballard, who became frustrated with his Homeland Security job when the federal government said that children from other countries couldn't be rescued, started Operation Underground Railroad in 2013. With former Navy SEALs, CIA agents and other experienced operatives, he trains foreign law enforcement agencies and then acts as one of the American lures to bring traffickers out of the shadows, as a presumed tourist in bars or on beaches. Some of the organization's exploits are featured in a recently released movie, "The Abolitionists," documenting the preparations, the contacts and then the takedowns of sex traffickers.

Utah Attorney General Sean Reyes took a trip to Colombia with Operation Underground Railroad in 2014, and because he spoke Spanish played the role of the "muscle" in a group of undercover Americans claiming to want dozens of child prostitutes for a permanent sex tourism hotel. The traffickers brought more than 50 children. "It was so fulfilling," Reyes said, "to see their faces when we liberated them. They were all singing and crying. That changed my life."

Ballard said Operation Underground Railroad works with U.S. embassies in host countries to find reliable law enforcement, and will not enter a country until it knows the victims will have follow-up care. Jessica Mass, the director of after care for Operation Underground Railroad, said she had just returned from vetting five after-care homes in a country that her group is targeting for a raid.

"I'm talking with the directors" of after-care homes, Mass said, "seeing how the girls are doing. We look for mental health services, education and vocational training." The organization also provides financial help, hires social workers and pays them fair wages, and buys supplies, beds and even roofing for homes that will take in underage sex workers.

"After care begins at the moment of rescue," Burkhalter of IJM said. "The social worker goes with the police and investigators of the mission."

Matt Parker, the founder of The Exodus Road in Colorado Springs, said that his group does try to help victims after raids, but that "we're not an after-care organization. There's many more after-care nonprofits" in the countries where they work, he said, that have more expertise.

Parker and Burkhalter noted that local governments have the first say on where and how freed victims are treated.

Parker said that Exodus Road has after-care staffs in two countries, but that their core competency is in investigating and arresting traffickers. "We've freed 736 men, women and children, and arrested 256 traffickers," Parker said. "The most powerful thing to do to fight trafficking is to make trafficking a dangerous thing to do."

Burkhalter seconded that. "You don't have to prosecute everybody," she said. "Prosecute a few and it really does start to lower the prevalence." She said that IJM began working with the Cambodian government in 2003, and that after 10 years, less than 1 percent of the victims were minors, and none were younger than 14. IJM has now disengaged from Cambodia, she said, confident that authorities there "really began to own it."

Paul Holmes, a former Scotland Yard detective who trains police forces worldwide in human trafficking investigations, said he had "no objection to any organization entering the fray against trafficking."

But he questioned including untrained participants, such as LaRoche and Reyes, in rescue missions.

"None of these people can be described as appropriately trained professionals," Holmes said, "and should not be anywhere near a professionally managed undercover sting operation." Holmes added that "concerns also arise around the risk of entrapment on the part of the undercover operatives" posing as sex tourists, and that "seeking to buy the services of child victims of sexual exploitation would likely run into serious admissibility difficulties in many countries."

Convictions of human traffickers in other countries are hard to obtain as it is. In 2015, according to the State Department, only about one-third of the nearly 19,000 prosecutions worldwide resulted in convictions.

Ballard, who is going to stop acting as a lure himself, plans to stay in the rescue business. Burkhalter acknowledged that it does take years for the process to effect change.

"It took years to develop that core of professionalism" in Cambodian police, she said. "There were some good ones. There were some really bad apples. But they are professionally handling this issue. That's what 10 years of companionship can bring you."