'Wheel of Fortune' Jim Thornton: FBI Never Contacted Witness in Pedo Chatroom Scandal

The woman who says she saw disgraced 'Wheel of Fortune' announcer Jim Thornton in a pedophile chatroom on a plane has NEVER been contacted by the federal agency that would investigate such matters -- the Federal Bureau of Investigation -- TMZ has learned.

Sources close to the witness tell TMZ ... the LAPD told the woman the FBI would be in touch with her, but so far the feds have been radio silent.

As for the FBI ... the agency is maintaining the same position it's held from day one, with a rep telling us Friday ... "The FBI does not, as a matter of policy, confirm or deny the existence of investigations."

TMZ broke the story in September ... the passenger snapped cell phone pics of Thornton's laptop screen containing chatroom messages about "cute boys" and a "hot little girl." Another message stated it was an "All-you-can-eat Boyfett," referring to a restaurant where they could find underage children.

The incident occurred during an American Airlines flight from Charlotte to L.A. in May -- and the passenger -- who was grossed out by what she was seeing -- kept taking photos of the group chat. One of the messages even referenced "CP," which the passenger believed stood for child porn.

When she had had enough, the passenger informed a flight attendant and shared her photos with the crew. Our sources say the captain then notified authorities, and law enforcement was waiting when the plane landed at LAX.

Our sources say the passenger gave a full statement to the LAPD officer, who said her information would be forwarded to the FBI, which would be in touch with her. Our sources say that never happened.

We're also told authorities briefly questioned Thornton, but he left without being arrested or charged. His lawyer says Thornton "did nothing wrong" and left the chat when he realized what it was.