Nearly three-quarters of online adults now use a social networking site of some kind with Facebook the dominant platform, a survey found. Seventy-three percent of Americans over age 18 on the Internet use at least one social network, the Pew Internet & American Live Project said in a release Monday. However, a significant number of users are now diversifying onto other platforms and about 42 percent of online adults hop on multiple social networking sites, the survey found. While Facebook is the preferred network, used by 71 percent of online adults, platforms such as Instagram, Pinterest, LinkedIn and Twitter are making gains, Pew said. Facebook use rose from 67 percent a year ago. Facebook and Instagram drew high levels of "user engagement," with a majority of users checking in on a daily basis, the survey indicated. Facebook owns Instagram. The report is based on telephone interviews with 1,801 adults age 18 and older conducted Aug. 7 to Sept. 16. The margin of error is estimated at plus or minus 2.6 percentage points.