On a hot September evening, streams of partygoers poured into an otherwise nondescript warehouse in Brooklyn. Awaiting them inside were 29 rooms pulsing with lights, music, and interactive, experiential art ripe for the Snapchat set. Stacy London, from TLC's beloved TV show What Not to Wear, posed for photos holding giant posters inscribed with "Love Wins" affirmations. A room called "The Sidewalk Is Your Runway" provided a West Village backdrop for shareable GIFs of attendees posing with a Michael Kors bag. And in one room, a neon light-up dance floor flashed, powered by the movements of partiers jiving to exclusive tracks from the singer Tinashe.

The soiree, aptly dubbed "29Rooms" and hosted by the women's media brand Refinery29, celebrated the kickoff of Fashion Week. And if you stood in one place long enough, you might spot celebs like Jessica Alba, Rashida Jones, Alexa Chung, and Entourage's Adrian Grenier sipping signature cocktails with names like #NoFilter or LBD (Little Blackberry Drink). You might say that the media outlet, which started as a discovery website for up-and-coming designers, has arrived. And you wouldn't be wrong.

After a decade of slowly honing its business model, Refinery29 is growing quickly. Founded by Justin Stefano, Philippe von Borries, Piera Gelardi, and Christene Barberich, it was the fastest growing media company on the Inc. 5000 in 2012 and 2013, and has made the list every year since. Coming in at No. 928 this year, it pulled in $80 million in revenue in 2015. A year ago, Refinery29 opened its first international office in the U.K. And in August, it closed $45 million in a second round of investment lead by cable giant Turner, placing its valuation at $500 million. The founders are dreaming big, talking of offices all over the world and their desire to bring a voice to women in oppressed communities.

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Becoming a media powerhouse hasn't always been easy--nor was it even part of the plan at the outset. In the early days, high school buddies Stefano and von Borries featured under-the-radar New York designers and artists with "29 best" lists (hence the name). Gelardi, von Borries' then-future wife, joined as the site's creative strategist and brought on Barberich, a former editor at City Magazine where Gelardi had worked as an intern, to oversee editorial. The four founders say they were obsessed with reading social-media mentions and comments in those days, and that's what led to the company's evolution into a media brand. Listening closely to their audience and meeting requests for new content topics or more diversity, forced Refinery29's leadership to retool over time. And in true outsider entrepreneur fashion, the site found its footing with a, at that point, rising market: a generation of women who feel misunderstood by mainstream media.

"We believe the world is sitting on a huge, untapped resource," says Gelardi. "And that's women who have been unable to reach their full potential. By giving them the tools, resources, and visibility to do so, we're going to make a better world for everyone."

It's a grandiose mission for a company best known for fashion and beauty content. However, in an era where traditional publications are folding faster than you can say "meal kit delivery app," the company's track record--and its trajectory--is impressive.

Since it launched in 2005, Refinery29 has made bold strides to expand its content, covering topics that cater to the pieces of a woman's life other media outlets overlooked. Take, for example, the Month of Hair in August 2011. It was a simple idea: feature a different woman's natural hair, every day for a month. Gelardi used street casting to ensure a diverse range of ethnicities and hair types, and the team set up a studio in the basement of their office, then located on Leonard Street in Manhattan. For an audience used to seeing smooth, perfectly coiffed 'dos, the woman who worked in the gym across the street and one intercepted at a shop nearby more accurately represented their real life hair struggle.

"We did it for ourselves mostly, and for our audience, and that was a huge reason why beauty was such a successful category for us," Barberich says. "It wasn't about feeding into this expectation that women have to be perfect or married or thin or beautiful, and it was really fun and satisfying for us to explore the fringe of what everyone else was talking about with beauty."

As the brand grew and the founders got to know their audience better--they refer to their target reader informally as a single "she" in conversation--they say it felt like gaps in her life weren't being addressed. Consider the "Money Diaries," a series Barberich says has gained a lot of traction among readers. Each entry details, in first-person, exactly how a particular woman manages her money (see, for example, "A Week in NYC on a $46,000 Salary"). Money and sex in particular are topics Barberich says readers want to learn about as they build their lives. Refinery29's news coverage has matured as well to include global news stories as they relate to women, such as sex workers in Denmark, police shootings in the U.S., and Syrian refugees.

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But of course, the company has to make money, and in that sense it is much like any other media brand--selling ad space and creating branded content. (It nixed its e-commerce model in 2013 to focus on building a media and entertainment content platform.) Across its site and social platforms, Refinery29 boasts 331 million users, mostly in a highly desirable demographic to advertisers: Millennial women.

And premium brands are chomping at the bit to reach its audience. Just a scan of Refinery's 29Rooms party reveals brand partners like Ford, Fossil, and Perrier. Thanks to its latest partnership with Turner Cable--which owns channels like CNN, Cartoon Network, and TBS--Refinery advertisers like Calvin Klein, Glossier, and Warby Parker are set to ride the media company's wave of success to an even broader global audience. When they partner with brands, Stefano says, they provide insights and feedback from that audience to help companies understand what Millennial women care about most. "We have always treated that as part of the approach to being a consultant to brands and working with brands in crafting creative campaigns," von Borries told Inc. in a 2013 interview. "We don't see the world as being so split between advertising and content."