Pinterest's popularity in the United States has surged in the last year, particularly among women, according to a new study.
The social bookmarking service is now used by more than one-fifth (21%) of American adults, up from 15% a year earlier, according to a survey of U.S. social networking habits from Pew Research. That puts Pinterest slightly ahead of Twitter and Instagram, though all three are well behind Facebook.
See also: Pinterest Drives More Traffic to Publishers Than Twitter, LinkedIn, Reddit Combined
Pew's data suggests that Pinterest has experienced strong growth among women in particular. One-third of U.S. women now use Pinterest, up from 25% as reported in a similar study in February. Just 8% of men use Pinterest, though that's up from 5% previously.
The Pew statistics are based on surveys of 1,445 Internet users in the U.S., a relatively small sample size, though one that a Pew rep says is "quite sufficient" to be representative of trends in the country.

While Pinterest's user base in the U.S. appears to be growing, that doesn't mean it's grabbing users away from other social networks like Twitter and Facebook. Pew found that 42% of online adults in the U.S. use two or more social networks and nearly one-fifth use three or more social networks.
"People are diversifying their portfolios when it comes to [social networks]," Aaron Smith, a senior researcher at Pew, told Mashable. "The addition of a Pinterest user is not necessarily taking away a Twitter user or a LinkedIn user."
For the first time, Pew released a detailed matrix breaking down the most common overlaps between the major social networks:

Unlike the other four social networks included in the survey, Pinterest is not public (or part of a public company) and has yet to disclose detailed user numbers. Pinterest is reportedly valued at nearly $4 billion and it is expected to follow its competitors in going public at some point down the road.
Image: Karen Bleier/AFP/Getty Images