Poshmark, a mobile application for iPhones that allows users to download photos of apparel and accessories from one’s own closet, has launched Showrooms, which allow users to engage in real-time virtual shopping parties.

The Poshmark app launched in December 2011. Using a model similar to Instagram, users sell and buy from each other. They take photos of items they want to sell and upload them to the app, while buyers “follow” sellers to see what’s new. Sellers set the price, while Poshmark handles all the back office work to facilitate the sale. Poshmark earns a 20 percent commission for its work.

Showroom features themed parties that last two hours, a time period that the company said allows the fun to cross different time zones. One may be limited just to certain designer-branded merchandise, while another could specify office attire. In the “Posh Party” environment, users follow all participants to see what’s available to buy and in the process create their own social shopping network.

Poshmark was founded by Manish Chandra, who previously cofounded the first social shopping site, Kaboodle.

According to Chandra, the app initially listed a few hundred items a week. After just seven months it is up to nearly 30,000 listings a week. Users on average sell 18 items, and they set the price tag for each piece.

He said that the “number of users is doubling every six to eight weeks.” Currently there’s one purchaser out of every seven to eight users, and once individual users make a purchase, they often make multiple purchases on a regular basis. “There is a small, but growing number that has made more than 100 purchases in less than three months,” Chandra said.

Poshmark thinks it could become the primary shopping engine for the twenty- and thirtysomething demographic. Of all users, 70 percent are both buyers and sellers, with the average transaction price between $30 and $40.

Jeff Clavier of SoftTech VC said his firm had invested in Kaboodle and participated in the December 2011 $3.5 million Series A round of financing led by Mayfield Fund for Poshmark. He said, as an investor identifying next-generation commerce, he’s seeing a pattern of engagement that’s become intriguing and is typified by Poshmark.

“The level of activity [in this marketplace] has picked up pretty quickly, especially repeat buys,” Clavier said, noting that this is especially true for fashion-related shopping event sites.