Today marks the six-month anniversary of the launch of flash sale e-retailer Fab.com. And the home décor merchant has snagged a nice half-birthday present for itself—$40 million in new cash.

Investment firm Andreessen Horowitz led the funding round, and its general partner Jeff Jordan will join Fab.com’s board of directors. Jordan, formerly the CEO of online restaurant reservation company OpenTable, president of PayPal and general manager of eBay North America, also sits on boards of OpenTable, online dating service Zoosk and mobile gaming firm Booyah.

Jordan says his firm is investing in Fab.com because of its strong management team, impressive execution of its e-commerce site and use of social media to drive sales, and its ability to achieve such success so quickly.

“They’ve leveraged social extremely effectively and they leverage data as effectively as any company I’ve ever worked with—startup or not,” Jordan wrote in a blog post this week. “I’ve rapidly become a big Fab.com consumer, as the UPS man and my spouse can attest.  It’s as close to addicting as anything I’ve ever experienced in e-commerce.”

Fab.com morphed out of Fabulis.com, a social network for gay men that the company’s founders launched in 2010; they changed the focus to selling designer items for a limited time, and launched Fab.com in June. The company plans to use the funds to grow the company in 2012, with plans for new investments in operations, technology, social commerce and product expansion.

Since relaunching as a flash sale site in June, the retailer has secured 1.2 million members, with 600,000 signing up in the last two month, Fab.com says. The e-retailer attributes much of its success to its focus on design, from the aesthetic of its e-commerce site and mobile apps, to the products it sells. Its engagement with social media is also a contributor, Fab.com says, as more than 50% of its members have come from social sharing.

Internet Retailer editors selected Fab.com to be included in its Hot 100 list, an annual compilation of the most innovative e-retailers. Order your copy of this special issue here.