Social media is an important tool for informing and engaging communities -- but who exactly is using it today? A new Pew report gives an update on social media trends for 2013.

In Social Media Update 2013, Pew found that nearly three fourths of U.S. adults use online social networking platforms of some kind, and a majority (42% overall) use multiple social networks. Also, it appears that Facebook and Instagram generally hold the highest engagement potential -- since a majority of users on these sites check them on a daily basis.

"Facebook is the dominant social networking platform in the number of users, but a striking number of users are now diversifying onto other platforms," Pew noted. "Among those who only use one major social networking platform, 84% say that Facebook is the single site that they frequent."

Facebook is popular across a diverse mix of demographic groups -- but especially with women, people age 49 and under, households earning less that $50,000 per year, and urban dwellers. Its least popular with seniors.

Instagram (which is owned by Facebook) is especially popular with women, blacks, people under 30, and those with some college education.

Twitter is especially popular with non-Hispanic blacks and people under 30.