The ten most popular social networking sites -- MySpace, Blogger, Classmates Online, YouTube, MSN Groups, AOL Hometown, Yahoo! Groups, MSN Spaces, Six Apart Typepad, and Xanga.com -- collectively reached an unduplicated unique audience of 68.8 million in the U.S. during the month of April, an increase of 22 million over April 2005. Together, these top social networking sites attracted 45 percent of active U.S. Web users last month, according to the internet media measurement company.

"Social networking sites are the reality television of the internet," said Jon Gibs, senior director of media, Nielsen//NetRatings. "The content is relatively inexpensive for publishers to produce, and social networking is not a fad that will disappear. If anything, it will become more ingrained in mainstream sites, just as reality TV programming has become ubiquitous in network programming.

"However, again like reality programming, the concept of 'reality' alone, or in this case social networking, is not enough. In this competitive marketplace, sites also have to provide consumers with distinct content they can identify with," continued Gibs.

Top 10 Social Networking Sites, April 2006 - U.S. Home and Work Traffic

MySpace, which has attracted significant media attention of late, topped the list with 38.4 million unique visitors and a remarkable year-over-year growth rate of 367 percent.
Blogger took the No. 2 spot, garnering 18.5 million unique visitors and growing 80 percent year over year.
Classmates Online ranked third, with 12.9 million unique visitors and a 10 percent year-over-year increase.
Newcomer YouTube and the more established MSN Groups rounded out the top five, with 12.5 million and 10.6 million unique visitors, respectively.
Rounding out the Top 10: AOL Hometown with 9.6 million, Yahoo! Groups with 9.2 million, MSN Spaces with 7.2 million, Six Apart Typepad with 6.7 million, and Xanga.com with 6.6 million.
Source: Nielsen//NetRatings, May 2006. This is a custom category and does not appear in Nielsen//NetRatings's syndicated service. Tekrati has rounded some numbers upward.

Are users fickle or loyal? Stay tuned...

Nielsen//NetRatings said the interactive nature of social networking sites keeps U.S. visitors coming back. MySpace enjoyed the highest retention rate among the group, with 67 percent of all March at-home visitors returning in April. MSN Groups and Facebook also benefited from a loyal following, with 58 and 52 percent of visitors returning month over month, respectively. Xanga.com and MSN’s new social networking site MSN Spaces rounded out the top five sites ranked by retention rate, with 49 and 47 percent, respectively.

"The social networking sites that are seeing strong growth have developed a unique online presence that is continually refreshed by user generated content," said Gibs. "This promotes ongoing consumer interest and visitor loyalty. However, while these sites have seen explosive growth over the past 12 months, this is a fickle youth audience, and the masses that have rushed to these sites, could turn their attention elsewhere. The question that remains is how strong are the social networks that consumers are building on these sites?"