(Pew Internet & American Life Project)

If you're increasingly finding elderly relatives liking your Facebook posts or retweeting you, you're not alone. The social networking site adoption rate for Americans 65 and older more than tripled in the last four years (up to 43 percent in May 2013 from 13 percent in the spring of 2009) according to a new survey from the Pew Internet & American Life Project.

But even with that increase, seniors are less likely than other age groups to use social networking sites. Pew's research shows 72 percent of U.S. adults use social networking sites as of May 2013, including nearly 90 percent of 18-29 year olds.