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The FBI and a young sextortion victim launched an ambitious public campaign Tuesday to find hundreds more potential victims of a Florida man who's already been sentenced to 105 years behind bars.

Lucas Michael Chansler, 31, of St. Johns, Florida, pleaded guilty last August to nine counts of producing child pornography in a scheme in which he'd target teenage girls on social networking sites and record them exposing themselves.

Then he'd blackmail them into giving him more graphic images and video, threatening to send the material to their friends and families. Authorities found more than 80,000 images and videos on Chansler's computer.

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Larry Meyer, a special agent who investigates crimes against children from the FBI's Jacksonville, Florida, division, said that so far, the FBI has identified 109 of Chansler's victims — but there are likely hundreds more in as many as 26 states, Canada and Great Britain. All of the girls were ages 13 to 18, he said.

An FBI map plots the locations of Lucas Chansler's known sextortion victims. FBI

Why did Chansler target underage girls? "One of the comments he made was that older girls wouldn't fall for his ploy," Meyer said.

Most of the known victims can't be identified because they're juveniles, but one of them, Ashley Reynolds is now 20, and it was her parents' call to the National Center for Missing & Exploited Children — after Chansler targeted their daughter when she was 14 — that began the investigation.

Reynolds has since become a prominent advocate for sextortion victims, saying she wants to make sure other girls don't make the same mistake she did.

"This ended for me," she said, but for many of Chansler's victims, "this never ended for them."

"High school girls never think it will happen to them," she said. "I never thought this would happen to me, but it did."

The FBI asked other victims of Chansler — and anyone with information that could help identify them — to complete a confidential questionnaire at fbi.gov/sextortion. They can also call 800-CALL-FBI (225-5324), email fbi.victimassistance@ic.fbi.gov or visit a local FBI field office.