WEST HOLLYWOOD, Calif. — As I sat in the lobby of a drab office building here, waiting to be led up to the penthouse loft of Tinder, the fast-growing dating app, I noticed that every few minutes young women would walk into the foyer, dressed in flip-flops, T-shirts and tattered jean shorts, and then go through a radical transformation.

Swapping out their rubber sandals for stiletto heels, they smeared on globs of lip gloss and flung on leather jackets. After a 30-second wardrobe change, they were ready for their appointments at a modeling agency on the ground floor. Same people: two very different personas.

A short elevator ride later, as I sat in on a meeting with a group of Tinder executives, it became clear that the quick-change act I had just witnessed downstairs, though unrelated to Tinder, still had a lot to do with what was going on upstairs. What someone wears, along with other visual clues given off in photographs, can tell a thousand different things about them.

And Tinder believes that these clues are the key to online dating.

In the two years since Tinder was released, the smartphone app has exploded, processing more than a billion swipes left and right daily (right means you “like” someone, left means you don’t) and matching more than 12 million people in that same time, the company said. Tinder wouldn’t share the exact number of people on the service, saying only that it was on par with other social networks at two years in operation. But a person with knowledge of the situation told me that it is fast approaching 50 million active users.