More than half of all American youth online are using social networking sites, according to a national survey.

The study found 55 per cent of youth between the ages of 12 and 17 who go online were using social networking sites such as MySpace and Facebook, according to a survey of teenagers conducted by the Pew Internet & American Life Project.

Older teens, particularly girls, are more likely to use these sites. Seventy per cent of teen girls aged 15 to 17 had profiles on social networking sites, compared with 57 per cent of boys in that age bracket.

For girls, the sites were primarily used as a reinforcement of pre-existing friendships. For boys, the sites were seen as a way to make new friends, the study found.

"Most teens realize how much of social life is happening in these networks — and that's something they often want to be a part of," says Amanda Lenhart, a senior research specialist at Pew.

Younger children were the least likely to do so, with just over a third of 12- and 13-year-olds saying they'd created a profile. Experts say this is partly because sites such as MySpace require users to be 14.

Most teens aware of security issues

Social networking sites allow online users to create a profile and build a personal network to connect to other users.

The popularity of the sites has caused concern among parents and schools who fear the risks of allowing teens to post personal information for public consumption.

The survey found teens were generally careful: two-thirds of those who created a profile say it is not visible to all internet users.

"One of the things to take away from this report should be a sense of 'the kids are all right,'" said Steve Jones, a communications professor at the University of Illinois at Chicago who studies new media.

"It's clear that teens are not just willy-nilly using social networking sites and making themselves vulnerable to predators.

"That is not to say, of course, that there are not some who are careless or even some who seem to invite trouble," he added, noting that many young people appear to be aware of security.

The survey of 935 U.S. youth, aged 12 to 17, was done by telephone in October and November. The results have a margin of error of plus or minus 3.7 percentage points.

The popularity of social networking among older teens highlights another growing trend, as social networking sites are increasingly becoming more popular with older users.

An earlier study by ComScore Media Metrix found teens made up only 12 per cent of MySpace users, down from 25 per cent just a year earlier.

The study published in October found more than half of the site's users were 35 and older.

With files from the Associated Press