LONDON, Aug 31 (Reuters) - Venture capital firm Accel Partners is investing 37 million euros ($47 million) to buy a minority stake in France's Showroomprive.com, one of a number of fast-growing members-only online outlets for designer goods.

Showroomprive.com

Accel, which has previously backed Facebook, Baidu and Admob, said the investment would complement its interests in other social commerce sites. These include Groupon, a site that offers daily deals to groups of a certain minimum size.

Accel said it was acquiring a significant minority stake but declined to elaborate.

Showroomprive.com is France's second-biggest private-sale site after vente-privee.com, in which private-equity firm Summit Partners bought 20 percent in 2007.

Such sites allow fashion houses to sell excess inventory at large discounts without damaging their brand by selling to a limited group of people. Often, new members have to be introduced by existing members of the club.

In the United States, invitation-only sites such as Gilt Groupe, Rue La La and Ideeli are thriving.

Showroomprive.com has 5 million members and made revenue of 75 million euros last year by selling goods from the likes of Calvin Klein, Dolce & Gabbana and Timberland. Chief Executive Thierry Petit says the company is profitable.

Thierry Petit

He plans to use the proceeds for expansion to build a new warehouse and possibly for acquisitions. The company is already active in Spain and wants to expand into Britain and Germany, Europe's most active e-commerce markets.

Petit says France is fertile ground for private-sale sites, since stores only hold sales at certain times of the year -- unlike other countries such as Britain, where sales are practically all year round.

"You could lose a lot of money in the UK," Petit told Reuters in a telephone interview. "To do it by ourself could be too ambitious," he said, adding that Showroomprive.com may seek a partner instead of buying a company or expanding by itself.

(Editing by David Holmes) ($1=.7911 Euro)