“We’re democratizing fashion,” says Jess Lee, CEO of Polyvore, the most popular fashion site on the Internet. More than 13 million unique visitors a month choose from 45 million product images to create “sets”–collages that look like fashion magazine pages, with every item available for purchase. That’s made Polyvore a shoppable magazine, where every month is September. (Take that, Vogue.) “We’re giving people, not fashion editors, the voice to define taste,” says Lee.

The industry likes what it sees, and partnerships helped push Polyvore into profitability in 2011. Bergdorf Goodman, for instance, asked users to style fashion director Linda Fargo for New York Fashion Week; the winner scored a seat at the Michael Kors show. American Eagle challenged users to make brand-specific sets, the best of which appeared on its Times Square billboard. “There are few places that offer this kind of targeted demographic, as well as the tools to interact with them,” says Oliver Walsh, CEO of digital marketing firm Wednesday, which worked with Polyvore on a campaign for the launch of Versace for H&M.

“We want brands to view us as a place full of their fans and influencers,” says CTO and cofounder Pasha Sadri. To that end, last fall it introduced the Polyvore Intelligence Report, a monthly set of analytics that breaks down the demographics of Polyvore users and tracks their top trends and items. The report is sent for free to select retailers, designers, and editors, revealing what shoppers want now. (Hot: fisherman sweaters and studded handbags!) Next up for eager shoppers? Sites dedicated to weddings and interior design.

Illustration by James Taylor