Another popular site YouTube.com, which focuses on people sharing video, doubled its traffic from April to 12.6 million visitors in May, ComScore Networks said. MySpace.com, a favorite of teens and young adults, had 51.4 million unique visitors last month, compared with 48 million in April.
The popularity of social networking wasn't expected to wane in the near future in the United States or the rest of the world, ComScore said.
"The challenge for social networking sites will now be monetization and how advertisers will respond to the global marketing potential of these sites," Peter Daboll, president and chief executive of ComScore, said.
The top five sites were No. 1 MySpace.com, followed in order by Classmates.com sites, FaceBook.com, YouTube.com and MSN Spaces.