Fashionistas jonesing for a high-end designer fix now have a discount online dealer—if they can score an invitation.

Gilt Groupe, an invite-only designer sample sale web site, on Wednesday said it raised $5 million in its first round of funding from Matrix Partners. Other investors include Gilt Groupe Chairman Kevin Ryan and Dwight Merriman, former CTO and founder of DoubleClick.

“The sample sale truly is a phenomenon that generates mass hysteria in the city,” CEO Alexis Maybank said. Gilt Groupe is an “opportunity to take it to a national audience,” she said.

The company’s invitation-only sales make it “a very different kind of e-commerce model,” said Nicholas Beim, general partner at Matrix Partners (who will join Gilt Groupe’s board of directors as a result of the financing).

Gilt Groupe was founded in 2007 by longtime friends, Ms. Maybank, a former eBay and AOL executive, and CMO Alexandra Wilkis Wilson, a former Bulgari and Louis Vuitton executive. The team’s deep background in fashion and e-commerce made Gilt Groupe an attractive investment, said Mr. Beim.

According to Mr. Beim, this is a very open field with no significant competitors. However, Atlas Venture-backed koodos, based in London, is also going after the lucrative luxury market with its own private online sales.

Because membership is through invite only, the Gilt Groupe has put much of its marketing might in the hands of its members, said Ms. Maybank.

Rather than using paid-marketing channels, the company encourages members to invite friends. For each successful invite, Gilt Groupe credits members $25.

Currently in soft launch mode, the site registered 3,500 members in its first 8 hours and it has been adding thousands of members daily, she said.

From an investor stand point, the company’s viral marketing strategy is very attractive, said Mr. Beim. Viral marketing is free and this is a market where people love to email each other about deals, he said.

The private site also appeals to high-end designers who want to maintain the integrity of their brands by avoiding selling their items next to discount brands.

The e-commerce site features up to three designer-specific sales per week from the likes of Zac Posen and Alessandro Dell’Acqua. Similar to brick-and-mortar sample sales, the online sales last for a very limited time–24 to 36 hours. By limiting the time, the site taps into the competitive nature of discount shopping and aims to give shoppers the “thrill of the chase” online, said marketing and communications director Rachel Wolkowitz.

The startup’s first sample sales sold out within hours, said Ms. Maybank.

For those lucky enough to receive an invitation, the free membership has its privileges. Not only do members get to avoid the long lines and pushy shoppers associated with traditional sample sales, they are also privy to discounts of up to 70 percent off.

Gilt Groupe’s discounts don’t exactly make for guilt-free shopping though. A $2,900 Judith Ripka chalcedony gold ring was on sale for $1,740 on the site. On the more affordable end, a $265 Zac Posen polo sold for $80.

Currently, the site is focused on the female bargain hunter, but the company plans to expand into men's, children's, and home goods within a year.

Although it is invite only, the site has no cap on its membership numbers and it plans to grow aggressively, said Ms. Maybank.