For Fashion's Night Out last year, New York-based beauty entrepreneurs Katia Beauchamp and Hayley Barna hosted a few friends to mark both the shop-'till-you-drop event and their just-launched company, Birchbox.

"There was all this energy; how could we not want to be a part of it?" said Beauchamp, 28. "And we said next year, we'll start planning far ahead so we can do something bigger."

So two months ago the company, which offers monthly boxes of curated beauty samples for members, started talking to Scoop, the 15-year-old New York-based boutique chain. For this year's event on September 8, they created a special box of goodies for buyers who spend $150 in Scoop's NYC Meatpacking District and Dallas shops. (Birchbox also is selling a limited number of boxes online.)

"I think to be associated with Vogue [one of the founders of the three-year-old event] and brands like Scoop legitimizes us," said Beauchamp, one of Inc.'s 2011 coolest entrepreneurs under 30. "And it puts us in front of new customers."

And did it ever: Scoop's Meatpacking outpost is at one of the event's hubs, with designer Zac Posen DJ'ing next door, an Alexander McQueen boutique scavenger hunt across the street, and hordes of revelers walking by decked out in sequins and their highest heels, treasure-hunting the coolest limited edition goodies (and the next free cocktail).

"Oooh, samples," squealed Sara Wilcox, a 24-year-old student wearing glittery platform heels and examining the contents of the Birchbox her friend had just received. She said she'd never heard of the company, so she pulled up the website on her iPhone. "It's like getting a bunch of little presents every month. I could buy that." 

In just three years, Fashion's Night Out—or FNO, as the industry refers to it—has grown from a one-time-only event to get people excited about buying clothes during the recession into an annual global shop-a-thon with an important place on the calendar for retailers from multiple industries.

"It's a day now like Mother's Day or Valentine's Day," says designer Diane von Furstenberg, whose bustling Meatpacking shop featured blended drinks from Los Angeles's Coffee Bean & Tea Leaf and a performance by R&B artist Estelle.

Shoe designer Stuart Weitzman held court in his Madison Avenue flagship with actresses Hayden Panettiere and Michelle Trachtenberg.

"Fashion's Night Out is like a big welcome back party," he said. "I think people are still excited about shopping and the celebrities and events around town—that's why FNO has remained a must-attend night." (Weitzman's event had a charity component: He was launching a Young Hollywood Cares Collection for ovarian cancer research, with shoes designed by Panettiere and Trachtenberg, plus Scarlett Johanssen and Olivia Palermo.)

"For entrepreneurs, it's become critical," says retail analyst Marshal Cohen. "It's a way to showcase your product, to showcase your store, to get your brand to resonate with the consumer. Word of mouth is such a key factor in how you grow your business, and this is a big night to do it." (Get tips on how to stand out at fashion week.)

The first Fashion's Night Out—the brainchild of Vogue editor Anna Wintour and von Furstenberg, president of the Council of Fashion Designers of America (CFDA)—was held in 2009. To get in on the late-night-shopstravaganza, participating brands had to promise not to launch sales during the event; the idea was to end the vicious recession-cycle of deep discounts. (There was nothing to stop savvy shops from displaying racks that were already marked down.)  

The first year saw 11 countries and some 700 stores in the U.S. take part, to measurable effect. Participating retailers nationwide saw store traffic increase 3.4 percent, with a 48 percent increase in New York City, according to ShopperTrak figures. NYC & Co, the city's marketing and tourism organization, surveyed some 1,300 shoppers, finding that 75 percent of them bought something that night. Two-thirds visited stores they'd never shopped in before, and 61 percent ventured to neighborhoods outside their work and living areas.

This year, 18 countries, more than 250 U.S. cities, and some 1,200 New York City retailers took part. The year also marked the event's debut online, where 200 retailers signed on. And creative partnerships abounded: The Hester Street Market, for example, set up shop on Henri Bendel's third floor. The exclusive uptown shop got an infusion of Lower East Side street fair cool, while young artisans and chefs got a chance to put their goods in front of new customers.  

What's driving FNO's growth?

Three things, says Cohen. First, women made big concessions in spending during the recession, and women make 70 percent of the purchases.

"Women are critical to retail, and they've been putting their fashion urges on hold," he said. "Fashion's Night Out is a time for passionate purchases."

Second, FNO brings back the idea of shopping as a social activity—that is, shopping as event or "shoptainment," as Cohen calls it.

And finally, in the era of flash sales, the evening taps into the idea of taking advantage of a limited opportunity to get something special. (There's no turning up fashionably late on the evening; many freebies, such as Marc Jacobs tote bags, are for the first customers, and there are finite numbers of designer goodies, such as the Alexander McQueen crystal skull key ring.)

Donna Karan, greeting guests at the door of her Madison Avenue boutique, called it a "celebration of fashion," but businesses of every type are vying for a piece of the action—and the profits.

Besides the clothing and beauty brands attempting to one-up each other with freebies, celebrities (Dolce & Gabbana nabbed Justin Bieber), and social media promotions and scavenger hunts, nonglossy companies such as Band-Aid have found ways to hitch themselves to the event. The first-aid giant teamed up with designer Cynthia Rowley to solve fashion emergencies. The "Glambulance" consisted of a hair stylist, a makeup artist, and first aid kits with (you guessed it) Rowley-designed bandages, embellished with lace and sequins. Quirky crockery retailer Fishs Eddy launched Todd Oldham-designed dinnerware. Even gadget purveyor Brookstone got in on the act, offering free massages and chargers for phones and iPods.  

And while Manolo Blahnik commandeered a milkshake van and Opening Ceremony lured shoppers with Mexican wedding cookies from foodie favorite Momofuku Milk Bar, savvy food and drink entrepreneurs seized the opportunity to do more than just cater the parties.  Cupcake chain Crumbs (No. 642 on the 2011 Inc. 5000) and Magnolia Bakery for the second year went head-to-head with special FNO-only charity cupcakes. Crumbs offered a white chocolate brownie body and vanilla cream cheese icing; Magnolia topped its classic vanilla and chocolate cupcakes with pastel-colored icing images of shoes and dresses. Meanwhile, 150-year-old Parisian pastry shop Laduree, which opened its first New York outpost two weeks ago, seized on FNO as the night to launch a New York-inspired flavor (cinnamon raisin) of its signature confection, the macaron. (Read more on the cupcake wars.)

Dylan Lauren, the CEO of Dylan's Candy Bar, asked 17 Rhode Island School of Design students to use some of the 7,000 types of sweets found in her shop to create edible versions of Rockport shoes for the window displays. The flagship also offered customizable shoe cookies for fashionistas craving a bespoke sugar high.

FNO "makes people excited to be back in the city…and gets people from all parts of Manhattan and outside who may not normally shop in your area to come and come back after [the event]," said Lauren.

With so much competition, how can a small business compete?

"It's easy not to do anything because you think you'll get lost, but if you don't do anything you'll get lost even further," said Cohen. "You have to try. Do something earlier. Do something later. Link up with another brand. You've got to try to get a piece of the action. You have to start somewhere."

Birchbox's Beauchamp says any effort is going to help. "Actually meeting customers and rallying them: That's how we learn a lot," she says. "Fashion Week is this hand-selected group of people going to the shows and getting invited to the parties. But Fashion's Night Out is about valuing customers and shopping and partnering with big brands to get in front of a customer."

Cohen's criteria for measuring success: "Did you get people to do things they normally wouldn't have done? Did you get them into your boutique on a Thursday night? Did they come back another time? Did you meet new people?"

He added: "It's not about size. Everyone can get in on this."