More than half of all Internet-using American teenagers use social networking sites, research suggests.
The study for the Pew Internet Project involved 935 teenagers and found 55% of American youths aged 12-17 had accounts at sites such as MySpace and Facebook.
It found that the sites were more popular with older teenage girls who tend to use them to keep in touch with their existing friends.
By contrast, boys were much more likely to use the sites to find new friends.
Websites such as MySpace give users a chunk of webspace they can personalise with images, video and blog entries.
To this they add a messaging system that lets members keep in touch with friends on the same network.
In the past few years these sites have become hugely popular among young people and some, such as MySpace, are by some measures challenging Yahoo and Google for the title of most popular site on the net.
The Pew research suggests that these sites were most popular with girls aged 15-17 as 70% of those questioned said they had an account at one or more of the social networking sites. By contrast only 54% of boys aged 15-17 were such keen users.
Some teenagers are avid users of the sites and 48% of those interviewed said they visited the sites on a daily basis and 22% said they looked at the sites several times a day.
Amanda Lenhart, a senior researcher at the Pew Internet Project, said the study was carried out to get a better understanding of how teenagers use these well-known sites.
"There is a widespread notion that every American teenager is using social networks, and that they're plastering personal information over their profiles for anyone and everyone to read," she said.
"Not every teenager is using a social networking website," she said, "and of those that do, more than half of them have in some way restricted access to their profile."
Most teenage social site users sent messages to friends to keep in touch and to make plans to meet socially, said Ms Lenhart.
The study questioned 935 teenagers in late 2006 to find out how they used the social networking sites.
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