Federal officials and advocates say online sex-related extortion against children is growing, and they are urging educators and parents to help raise awareness at back-to-school events.

They say they see a rise in so-called sextortion, which often involves adults posing as someone younger on social media to get minors to send them inappropriate photos or video. Offenders typically threaten to post the images they obtain - or send them to others - unless they are sent more explicit images.

"It's not uncommon," said Michelle DeLaune, chief operating officer at the nonprofit National Center for Missing & Exploited Children, based in Alexandria, Va. "It's something that we see every day, and it's something that's concerning because it can inflict a tremendous amount of damage on a child."

DeLaune's organization and the U.S. Department of Justice recently released a public service announcement showing a teenage girl blackmailed into providing explicit images by an older offender who pretends to be someone she knows.

FBI officials say offenders often approach children and teenagers - typically ages 10 to 17 - on social networking sites but then convince them to move to anonymous messaging apps or video chats.

"They look to transition them to a more secluded form of communication," said Ray Duncan, assistant special agent in charge of the criminal division of the FBI's Washington Field Office.

Increasing reports of sextortion led the National Center for Missing & Exploited Children to conduct a recent study of 800 sextortion cases, finding that 78 percent of the victims were girls, with an average age of 15, DeLaune said.

In 6 percent of cases examined, the offender threatened to distribute the images if the child did not meet them in person.

"The threat and the impact of these situations is significant," DeLaune said. "The children find themselves in situations they don't know how to get out of."

FBI officials say there is no reliable data reflecting the full extent of the phenomenon, but they have seen an increase of sextortion against children in recent years and are working with state and local authorities to improve awareness. The crime is underreported, they say, because many victims are too embarrassed to come forward or fear being charged with child pornography.

An FBI report this year that included a survey of law enforcement officials and others involved in child exploitation cases found sextortion was "by far the most significantly growing threat to children, with more than 60 percent of survey respondents indicating this type of online enticement of minors was increasing."

Duncan noted that a 2015 analysis of 43 sextortion cases with child victims found suicides or attempted suicides in at least 28 percent of the cases examined. "It can exact a pretty large psychological toll on the kids," he said.

Sextortion is part of a broader problem of online sexual exploitation. The National Center for Missing & Exploited Children says that in the past 18 years its CyberTipline, a national hotline, has fielded more than 90,000 reports of alleged instances in which an individual has attempted to groom or lure a child for sexual purposes during online communication.

In Maryland, for example, a recent case pointed to potential dangers for teenagers who meet adults through social media. A 14-year-old girl met a man she knew as "Jay" through social media and agreed to meet him after a week of communicating, according to court documents.

On Aug. 20, the man allegedly picked her up near her home and drove her to his home, 45 minutes away, court documents say. The man, Onaje Robinson, 42, allegedly turned on a Netflix movie and had sexual intercourse with her, according to the court filings.

The girl described the sex as non-consensual and said Robinson used a stick to hit her during the encounter, the documents say. Robinson, an assistant girls' track coach at a local high school, faces sex offense and assault charges. He told authorities the sex was consensual and that he thought she was 20, court records state.

Robinson turned himself in last week and was released on a $10,000 bond, court records state. He could not be reached for comment.

Federal officials listed tips they said could help prevent sextortion:

- Making children aware that anything they share online may be viewed and used by others

- Ensuring children's apps and social networking sites' privacy settings are set to the strictest level possible

- Reviewing all apps downloaded to smart phones and mobile devices and monitoring activity on those devices

- Reviewing "friends" and "followers" lists to delete those a child has not met in person.

- Ensuring that anyone who asks a child to engage in sexually explicit activity online is reported to a parent, guardian or law enforcement official promptly.

DeLaune added another bit of advice: "We encourage adults to create an environment where a child would feel comfortable coming to them if they find themselves in a situation where they feel uncomfortable or afraid."