About 13% of online adults in the U.S. also use Twitter, according to a new report released Wednesday by the Pew Research Center.

That's up from 8% about six months ago -- a testament to the 5-year-old social networking site's growing popularity.

More than half, 54%, of the adults who use Twitter send their tweets using a cellphone, Pew said in the update to its ongoing Internet and American Life Project study.

And, just as the Pew center found last year, Twitter is particularly popular with minorities.

"In November 2010, there was an 8 percentage point difference in Twitter use between African American and white internet users (13% for blacks vs. 5% for whites)," Pew said in its report. "By May 2011, that gap was 16 percentage points -- 25% of online African Americans now use Twitter, compared with 9% of such whites."

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