A comScore Media Metrix analysis of the user bases of leading social networking sites reveals significant age differences among them.

Users of MySpace.com and Friendster.com generally skew older, with people age 25 and older constituting 68 and 71 percent of their user bases, respectively, according to comScore. Facebook.com, which began as a site for college students, has a younger user base: 34 percent of Facebook users are 18-24 years old, approximately three times the representation of that age segment in the general internet population. Xanga.com has a younger user profile, with 20 percent of its users age 12-17, about twice as high as that segment's representation in the total internet audience.

"There is a misconception that social networking is the exclusive domain of teenagers, but this analysis confirms that the appeal of social networking sites is far broader," Jack Flanagan, EVP of comScore Media Metrix, said in a statement.

As MySpace.com has undergone dramatic visitor growth, it has become more popular among older users. The most significant shift has occurred among teens 12-17, who accounted for 24.7 percent of the MySpace audience in August 2005 but today represent 11.9 percent of the site's total audience. Internet users between the ages of 35-54 now account for 40.6 percent of the MySpace visitor base - 8.2 percentage point than last year.

"While the top social networking sites are typically viewed as directly competing with one another, our analysis demonstrates that each site occupies a slightly different niche," Flanagan said.