The president and the GOP presidential candidates have tapped into the powers of social media to fuel the White House race. President Obama uses Google Plus. Twitter feeds are full of Republican primary schedules.

And, last week, on the most talked-about social media site of the moment, a Romney joined the reported 10 million-and-growing Pinterest fans.

It was not Mitt Romney who joined. It was his wife, Ann, who presents a glimpse into her tastes on digital pinboards: a love of “Anna Karenina,” a healthful banana-bread recipe and photographs of the New England Chapter of the National Multiple Sclerosis Society. The site allows users to “pin” images from around the Web into categories they create. Ann Romney’s photos of the MS Society events, for instance, are in a category called “Things I Love.”

Why Ann Romney, and not her husband, stepped in as the de facto pinner of the Romney campaign, is easily understood with a quick look at Pinterest’s audience: More than 60 percent of the pinners are women.

A few months ago, when the site to sample was Google Plus, the opposite was true. Early numbers claimed that nine in 10 Google Plus users were men. That prompted women to start campaigns — such as Women of G+ — to lure more to sign up.

Similar gender dynamics play out across the Web. Women use Facebook more. Men turn to LinkedIn. On the social news site Reddit, where users often post under pseudonyms, a common refrain is posted anytime a user identifies herself as female: “There’s a girl on Reddit!?”

Are social media sites destined to always be the online equivalent of a seventh-grade dance? Men on one side, women on the other?

The numbers suggest that, instead, women will soon overrun the dance floor of social media sites — and what’s more, be the DJs, too.

Since 2008, according to the Pew Research Center’s Internet and American Life Project’s Kathryn Zickuhr, women have led men in the use of social media sites. Women not only outnumber men on the sites (69 percent of women use social media, compared with 60 percent of men), they also spend more time on them.

For Johanna Blakley, who researches the impact of mass media as a professor at the University of Southern California, the predominance of women on social sites could lead to a positive, although subtle, change in the way women are represented in media. In a TED Talk on the subject last year, she spoke about her belief that social media will help “dismantle some of the silly and demeaning stereotypes that we see in media and advertising about gender.”

Thanks to sites including Pinterest, women can assert via pins, posts and updates who they are and what they want, rather than be mere observers of an advertising-fueled culture.

Women are moving from passive purchasers to online authorities and tastemakers. Gender differences remain, but some of the false stereotypes might die a death by a thousand pins.