Sources told the attorneys general that MySpace had discovered thousands of sex offenders on its site in an internal investigation, Blumenthal said. He did not give the identity of the sources.
"Our objective is to assure that these convicted sex offenders are removed from this site and other social networking sites," Blumenthal said by telephone after holding a news conference in Hartford, Connecticut.
"The information about convicted sex offenders on MySpace is simply more evidence that additional measures such as age verification are necessary to protect children," he said.
About 100 million people worldwide use the fast-growing MySpace service.
Children's advocates say they fear that young teens who use MySpace, Facebook and other such sites to socialize fail to grasp the risks involved in meeting people over the Internet.
"People should be notified if these offenders have been in touch with them or their children," said Judi Westberg-Warren, president of Web Wise Kids, a California-based nonprofit Internet safety organization.
In January, the families of five teenage girls who were sexually assaulted by people met through MySpace sued News Corp., charging negligence and fraud.
U.S. lawmakers are considering making it a crime for anyone over 18 to misrepresent their age for the purpose of luring a minor over the Internet for illegal sexual contact.
One concrete step MySpace and other social-networking sites could take to improve the safety of young people would be to verify the ages of their members, Westberg-Warren said.
"This is not just about MySpace, this is about all social networking," she said. "The kids can go from MySpace to another social networking site. This needs to be, in general, something that all social networking sites are working with."
The attorneys general of Georgia, Idaho, North Carolina, Ohio, Pennsylvania, Mississippi and New Hampshire joined Connecticut in signing a letter to the company asking it to turn over information.
They also asked MySpace, which has come under criticism for not doing enough to protect young people using the site from adult sexual predators who pose as teens, if the profiles in question have been removed from the site.
MySpace officials could not provide immediate comment.
