WASHINGTON - ADULT Americans who use the Internet are joining social networks at a rapid rate and the number with an online profile has quadrupled in the past three years, according to a new survey.

Thirty-five per cent of US Web users aged 18 or older have a profile on a social network such as Facebook, MySpace or LinkedIn, the Pew Internet & American Life Project survey found, up from just eight percent in 2005.

While the number of online adult Americans logging onto social networks is rising, they lag behind the number of online American teens who do so, the Washington-based Pew Research Center said in a report released on Wednesday.

Sixty-five per cent of online Americans aged 12 to 17 years old use social networks, it said.

Adults, however, still make up the bulk of American users of social network websites because they make up a larger portion of the US population than teens.

The survey found, not surprisingly, that the number of adults who use social networks declines with age.

Seventy-five percent of online Americans aged 18 to 24 years old belong to a social network; 57 per cent of those aged 25 to 34; 30 per cent of those aged 35 to 44; 19 per cent of those aged 45 to 54; 10 per cent of those aged 55 to 64 and just seven per cent of those aged 65 and older.

Fifty per cent of adult social network users have a profile on MySpace, the survey found, while 22 per cent have a profile on Facebook, six per cent have a profile on LinkedIn, two per cent have an account on Yahoo! and one per cent each have accounts on YouTube and Classmates.com.

Other adult users have profiles on sites such as BlackPlanet, Orkut, Hi5 and Match.com, Pew said.

Fifty-one per cent of adult social network users have two or more online profiles while 43 have only one online profile.

Eighty-nine per cent of the adult Web users surveyed said they use their online profiles to keep up with friends, 57 per cent said they use them to make plans with friends and 49 per cent said they use them to make new friends.

Sixty per cent of adult social network users said they restrict access to their profile so that only their friends can see it while 36 per cent allow anyone to see their online profile.

The survey found that men and women are equally likely to be social network users but men are more likely than women to have two or more online profiles (54 per cent vs. 47 per cent).

Pew said whites are less likely than African-Americans or Hispanics to have a social network profile.

Thirty-one per cent of online white adults have a social network profile, compared with 43 per cent of African-Americans and 48 per cent of Hispanics.

The median age of a MySpace user is 27 years old, the survey found, while the median age of a Facebook user is 26.

The median age of a user of LinkedIn, the professional networking service, is 40 and they are likely to be men, to be white and to have a college degree.

Thirty-seven percent of the adults surveyed said they visit their profile daily while 23 per cent said they visit every few days, 15 per cent once a week and 23 per cent less often than once a week.

Forty-eight per cent of teens visit a social network profile at least once a day, 32 per cent visit weekly and 20 per cent visit less often.

The data in the report was from separate surveys conducted between November 2007 and December 2008 with margins of error ranging from plus or minus three percentage points to plus or minus six percentage points. -- AFP