Fashionable scenesters like the model Hanne Gaby Odiele and the jewelry designer Waris Ahluwalia wandered the halls, checking out two dozen classrooms that had been transformed. In one, the restaurateur Serge Becker held a dance hall class with students in Jamaican uniforms. In another, the streetwear kings behind aNYthing installed a working skateboard ramp, while blond socialites in little white dresses looked on.  Orchestrating it all, wearing a blazer and white V-neck, was Olivier van Themsche, a former night life hot shot from Paris, who left France to make his mark in New York as an entrepreneur.  “Life was really, really easy for me in Paris,” said Mr. van Themsche, 35, whose streaks of gray hair add a touch of gravitas to his otherwise lighthearted demeanor. “But I needed something more.” So in 2010, he moved to New York City. “Coming here was really challenging for me: to go from being like the boss of the restaurant to going back to the kitchen where I had to roll up my sleeves and do the dishes.”  He didn’t exactly arrive alone and penniless. Mr. van Themsche is plugged into a very rarefied sliver of the New York social circuit, owing to his fancy upbringing and the wild outdoor parties he held at Les Jardins de Bagatelle in Paris, which attracted the likes of Dita Von Teese and Kanye West. Nowadays, he has intimate barbecues in the backyard of his West Village duplex, frequented by the descendants-of set like Eugenie Niarchos, the Courtin-Clarins sisters and Vladimir Restoin Roitfeld.  Those gatherings provided validation for a business idea. Mr. van Themsche noticed that his friends were shopping for vintage designer duds and furniture on sites like eBay and Craigslist, which he considers “the opposite of fashionable.” What if he could tap into his socialite network, and create a chic “social marketplace” featuring items curated by his friends.  The name of the site? Why, the Cools, of course.  The site, which officially started in June, looks a bit like Tumblr — a clean interface that allows users to scroll through eye-catching images of new and used clothing, home goods, artworks and tech gear. Instead of a “like” button, users can mark things as “cool” or “uncool.” More important, they can click “buy” and complete the transaction on the site.  Recent items include a baby blue Eames-style rocking chair for $80, and a 1973 BMW motorcycle for $9,999. About 1,500 sellers have signed on including Grey Area, which was started by Kyle DeWoody and sells limited-edited art objects, as well as everyday cool people who want to unload their Leifsdottir heels and Dries Van Noten sweaters.  “We’re not here to say what’s cool,” Mr. van Themsche said. “We’re here to offer a platform where anyone can say what’s cool.”  The Cools enters a growing field of socialite shopping sites like Lauren Santo Domingo’s Moda Operandi, but Mr. van Themsche has many powerful people rooting for him. In addition to raising $2.5 million from the media mogul Bob Pittman and others, he has an advisory board that includes the Fiat heir Lapo Elkann, the LVMH scion Antoine Arnault and the fashion designer Erin Fetherston. The SoHo office has a staff of 15.  “The fact that I am speaking with you about Olivier means that I truly think that what he is doing is clever,” said Mr. Elkann, who rarely talks to the media.  “When Olivier told me he was working on something, I trust this guy so much, I could’ve almost started advising without knowing what it was,” said Mr. Arnault, who has known Mr. van Themsche since elementary school.  Olivier van Themsche was born in Paris. His father, Didier van Themsche, ran a racing stable in Normandy that produced illustrious horses like Ourasi, and wanted his son to be a jockey, but Mr. van Themsche resisted. “I’ve been an entrepreneur forever,” he said.  He attended Stanislas, a well-known private school in Paris, before getting kicked out in his teens (“I was a troublemaker,” is all he would say). He went on to attend the Sorbonne, where he honed his party promoting skills, holding 2,000-person parties at Parisian clubs like Les Bains Douches and Chez Castel.  After college, he enrolled in business school in Paris, but he dropped out to run an electronic music label, Brif Records, with his childhood friend Gaspard de Dreuzy, and then a video game company, Polygon Studio. When Polygon went under during the 2001 dot-com crash, he started planning lavish parties for companies like Diesel and Rolex.  That eventually lead to the bacchanalian parties at Les Jardins de Bagatelle called Institut Bonheur (or “Institute of Happiness”), which ran for five years and attracted artists, musicians, bankers and aristocrats.  Mr. van Themsche’s party skills seem to have translated online. On the Cools, one gets the sense that you should be searching for a vintage Oscar de la Renta dress with one hand and smoking a Gauloise with the other. It only made sense, then, that Mr. van Themsche would kick off the site with a big party. “For me, the Cools is the meeting point of all my experiences,” he said.  As the party in June wound down and the last skater took his run, the crowd dissipated into the street. But the night was by no means over: the cooler kids were heading to an after-party at Le Bain.
From organizing lavish events for luxury brands and aristocrats, the night life maven, Olivier van Themsche, is trying his hand at a Web site.