A freelance American reporter who contributed videos to Agence France-Presse (AFP) in recent months was kidnapped in war-torn Syria six weeks ago and has been missing since, his family revealed Wednesday.

US journalist James Foley, 39, an experienced war reporter who has covered other conflicts, was seized by armed men in the northern province of Idlib on November 22, according to witnesses.

Foley who last supplied AFP with video material the day before he disappeared, was picked up in the town of Taftanaz by four men who later released his driver and translator, the witnesses said.

The reporter was travelling with another journalist who has also been reported missing, but whose family has requested that he not be identified.

No group has claimed responsibility for the abductions, in a country which has been racked by bitter civil war since the start of an uprising by rebels opposing President Bashar al-Assad's regime nearly two years ago.

Foley's family, which had earlier asked media groups not to report the abduction in the hope that a low profile would assist in efforts to free him, broke their silence Wednesday to reveal his plight.

"We want Jim to come safely home, or at least we need to speak with him to know he's okay," said John Foley, father of the missing reporter who also contributes to the US-based international news website GlobalPost and to major US TV channels.

"Jim is an objective journalist and we appeal for the release of Jim unharmed. To the people who have Jim, please contact us so we can work together toward his release."

The family has launched a website (www.freejamesfoley.org) and Facebook page (http://www.facebook.com/freejamesfoley) to highlight Foley's ordeal.

Foley was previously kidnapped and held for six weeks by forces loyal to slain Libyan dictator Moamer Kadhafi while covering that civil war last year.

At the time, he was working for GlobalPost which was involved in his rescue and which is standing by his family in the latest incident.

The reason for the men's abduction in Syria remains unclear. It is not known if their abductors are financially motivated or if they are linked to any Islamist groups, rebels or pro-regime forces or sympathizers.

Large parts of northern Syria are controlled by anti-Assad rebel groups that form part of the Free Syrian Army or are made up of jihadists, including foreign fighters.

Details of the kidnappings emerged weeks after high-profile US television reporter Richard Engel, who works for the NBC network, and his crew escaped after being held for five days by pro-regime militiamen in Syria's north.

Engel told his network that his team was seized while travelling with a group of Syrian rebels but that they managed to escape last month after two of their captors were killed in a firefight with the rebels.

AFP chairman Emmanuel Hoog said the organisation was doing its utmost to secure Foley's freedom.

"We are in constant touch with his family and loved ones, while reaching out to a range of contacts and doing everything we can to facilitate his release," he said.

"He is a professional journalist who is absolutely neutral in this conflict," Hoog said of Foley, who has contributed around 30 video stories to AFP since late March 2012.

"His kidnappers, whoever they may be, should free him immediately," he added.