Washington - The surge into social networks is gaining pace among Americans, with Facebook dominating but with many people using multiple platforms, a study showed on Monday.A Pew Research Center survey found 73% of Americans over age 18 on the internet use at least one social network - or about 63% of the total adult population.Facebook is the preferred network, used by 71% of online adults, or 57% of all American adults, according to Pew researchers.However other platforms like Pinterest, LinkedIn and Twitter are making gains, and a growing number of people are using multiple social networks.Pew found that 42% of internet users (or 34% of all American adults) use two or more of the five most popular social networks.Use of Facebook rose to 71% of online adults from 67% a year ago, the study found.A large part of the growth for Facebook came from older Americans: Roughly 45% of internet users over 65 are using Facebook, up from 35% in late 2012.Four other social networks, including Facebook-owned Instagram, are battling for the number two spot for US users.LinkedIn is used by 22% of online American adults and is especially popular among college graduates and those in higher income households. That is up from 20% a year earlier.Pinterest usage grew sharply to 21% of online adults, from 15% a year ago. Pew said that women are four times as likely as men to be users of the bulletin-board style social media platform.Some 18% of online adults use Twitter, up from 16% a year ago, Pew said, with adoption levels particularly high among younger adults and African-Americans.Instagram use rose to 17% of online adults from 13% a year ago, according to the survey. Much of this growth came in the 18 to 29 age bracket and among African-Americans.Pew found that Facebook and Instagram drew high levels of "user engagement," with a majority of users checking in on a daily basis.Some 63% of Facebook users visit the site at least once a day, and 40% do so multiple times throughout the day.That compares with 57% of Instagram users who visit the site at least once a day and 46% of Twitter users.The researchers also found considerable overlap among the leading social networks. For example, 93% of Instagram users also use Facebook, as do 83% of LinkedIn members.Some 53% of Twitter users also use Instagram, and 53% of Instagram users use Twitter, the survey found.The report is based on telephone interviews conducted from 7 August to 16 September among 1 801 adults age 18 and older. For the total group, the margin of error is estimated at 2.6% points and 2.9 points for internet users.