Teens have some of the highest social networking penetration of any age group. eMarketer estimates that 81% of internet users ages 12 to 17 will use social networks at least monthly this year, rivaling the 90% of online 18- to 24-year-olds and the 82% of 25- to 34-year-olds who will do the same.

Pew Internet & American Life Project, in partnership with the Family Online Safety Institute and supported by Cable in the Classroom, found in July that 16% of online teens used Twitter, doubling the 8% figure found in September 2009.

Teen girls were more than twice as likely as boys to use the microblogging service, at 22% vs. 10% of the respective populations. Moreover, black internet users were more than three times as likely as whites to do so, and also significantly more likely than Hispanics. Older teens were also more active, as were those with lower household incomes.

Source: eMarketer
http://www.emarketer.com/Article.aspx?id=1008690&ecid=a6506033675d47f881651943c21c5ed4&R=1008690