Nearly two out of five US adults use social media to get involved in politics, with the younger crowd and the ideologically committed especially active, a study showed Friday.

The Pew Research Center study showed that 60 percent of adults use social networking sites like Facebook or Twitter and that two-thirds of these -- 39 percent of all US adults -- use social media for civic or political activity.

Social media users who talk about politics on a regular basis or who have firm ideological ties are the most likely to be active on the sites, the study found.

And those aged 18-29 are "notably more likely than older users to have posted their own comments, as are those who have at least some college experience," Pew said.

"Now that more than half of adults use social media, these technologies have worked their way into the rhythms of people's lives at many levels," said Lee Rainie, director of the Pew Internet & American Life Project.

"At the height of the campaign season, it is clear that most social media users, especially those who care about politics, are using the tools to debate others, stay in touch with candidates, flag political news stories and analysis that are important to them, and press their friends into action. We'll see the fruits of this neo-activism on Election Day."

Around 35 percent of social media users have used the tools to encourage people to vote, the study showed, with Democrats (42 percent) holding an edge over Republicans (36 percent) and independents (31 percent).

Around a third post their own comments or thoughts, or repost content from someone else.

About 21 percent of those using Twitter or other social media belong to a group on a networking site that is involved in political or social issues, or working to advance a cause.