MySpace still commands a lead over Facebook overall and within individual age groups, but U.S. visitors under 18 to MySpace dropped 30 percent over the past year, while Facebook's rose about 2½ times.
In June, MySpace had 4.7 million U.S. users under 18, compared with 4.3 million for Facebook.
Both MySpace and Facebook showed growth in all other age groups. Overall, MySpace grew 35 percent to 70 million users, while Facebook doubled to 28 million.
In June, MySpace had a 10 percent share of all page views among those 12-17 (officially the minimum age for MySpace is 14; Facebook's is 13), compared with 12 percent a year earlier. Facebook increased to 7.0 percent from 3.1 percent during that period.
MySpace officials say the News Corp. (NWS)-owned site remains strong.
Facebook's growth is partly attributable to the fact that its numbers were low to begin with. Until late 2005, the site was closed to all but college communities.
Although MySpace and Facebook are both social-networking sites where users are encouraged to expand their circle of friends through personal-profile pages containing bios, photos and messages, they differ in their approach.
MySpace allows anyone to join and search for other profiles, though the company has since made it easier for users to keep portions of their profiles private.
Facebook, on the other hand, began as a college-only Web site, with users initially able to fully view profiles only from others on their own campuses; only later did Facebook expand to high schoolers and eventually to everyone.
Amanda Lenhart, a senior research specialist at the Pew Internet and American Life Project, said teens may perceive Facebook as safer, whether actually true or not, because networks are organized around real-world identity like high school affiliation.
FOXNews.com is owned and operated by News Corporation, which also owns and operates MySpace.com.