Firms are increasingly using such sites to promote their products and services.
Web research firm ComScore said UK-based Bebo.com became the most visited social networking site from within the UK in July, attracting 10.6 million unique visitors, an increase of 63% over the start of the year.
It was closely followed by US social networking behemoth Myspace.com, which enjoyed a 25% increase in traffic over the same time period, to reach 10.1 million visitors in July. Myspace was previously the number one site in the UK.
The fastest growing social networking site, however, was Facebook.com, which grew 366% since the start of the year, to attract an audience of 7.6 million visitors in July 2007.
HI5.com increased its UK-based traffic by 36% to 1.9 million unique visitors, while Faceparty.com grew 9% percent to 1.7 million.
Bob Ivins, an analyst at comScore, said, "Social networking sites like Facebook and Bebo have shown phenomenal growth over the past six months, and should continue to do so."