As the week progressed, dozens of similar scenes were being played out all around the city in the twice-yearly outdoor style show that competes, and indeed sometimes eclipses, the action on the runways. In front of Milk Studios, on the piers along the Hudson, and at other locations where shows were staged, scores of fashion hopefuls, mostly female, mostly young, preened for the cameras, apparently vying for their 15 seconds of fame on Instagram, Tumblr or one of the dozens of fashion blogs proliferating on the Web.

Was it only a couple of years ago that these showily outfitted swans — stylists, bloggers, fashion editors and style-struck students — click-clacked on the pavements, showing off a mash-up of vintage clothes, fast fashion and high-end labels in what used to be seen as a commerce-free zone?

Today many of them are Web icons, trotting out their finery for scores of fans. But what they are parading as street style — once fashion’s last stronghold of true indie spirit — has lately been breached, infiltrated by tides of marketers, branding consultants and public relations gurus, all intent on persuading those women to step out in their wares.

“These girls are definitely billboards for the brands,” said Tom Julian, a fashion branding specialist in New York City, one of a handful engaged in a particularly stealthy new form of product placement. “People still think street style is a voice of purity,” Mr. Julian said. “But I don’t think purity exists any more.”