Federal prosecutors said a Maryland man charged with extorting an Indiana teen into sexual favors victimized other teens after he was released on bond.Court documents filed Wednesday in U.S. District Court in Indianapolis said Trevor Shea, 20, of Mechanicsburg, Md., has agreed to plead guilty to charges of sexually exploiting children stemming from both cases.The documents indicated that Shea coerced girls in Florida, Kansas and Maryland into various acts after his release on bond following his initial indictment in June 2010. Shea had agreed not to use a computer as a term of release."The commission of those additional three counts while on bond carries the possibility of an additional 10 years imprisonment on each count. The federal courts take this reoffense while on bond very seriously," said Deputy U.S. Attorney A. Brant Cook.Shea could face 15 to 30 years in prison on each of the seven counts against him, and up to 30 years more for violating his pre-trial release terms.Shea's attorney, Michael Donahoe, declined comment.Prosecutors filed three counts of sexual exploitation of children against Shea on Tuesday in U.S. District Court in Indianapolis.Federal prosecutors called Shea's case an example of "sextortion," or when an Internet predator seeks out and gains access to children and teenagers to sexually exploit and terrorize them.A 16-year-old Brownsburg girl said her nightmare began with a party in 2009 in which three teenage girls with a webcam visited an Internet chat room and yielded to requests to flash their breasts.A week later, one of the girls started getting threatening e-mails, officials said. A stranger told the girl he had captured her image on the webcam and would post the pictures to her MySpace friends unless she posed for more explicit pictures and videos for him.On at least two occasions, the teen did what her blackmailer demanded, authorities said. Finally, police and federal authorities became involved and indicted Shea.The girl's mother called police when she found out about the threats. Authorities subpoenaed Internet service providers to track the chats and e-mails to their source, a computer in Maryland, according to court documents."Shea admitted to regularly using the Internet to seek out and persuade teenage girls to show their breasts on webcams, and at other times, frequented websites where webcam footage of of teen girls revealing themselves was posted by others," part of the plea agreement read.Authorities said last year that Shea told agents he had engaged in similar schemes with about 10 girls, most of them 17 or 18 years old.Federal prosecutors and child safety advocates said they're seeing an upswing in such cases of online sexual extortion. They say teens who text nude cell phone photos of themselves or show off their bodies on the Internet are being contacted by pornographers who threaten to expose their behavior to friends and family unless they pose for more explicit porn, creating a vicious cycle of exploitation."You want to keep that computer where it's out and visible in the family room," said Sharon Pierce with Prevent Child Abuse Indiana. "You want to know where they can access the Internet. Is it on their computer at home, or is it on the telephone, or the computer at school? There are so many facets to the Internet itself to keeping children safe."