With exits for start-ups seeming more distant than ever in the current economic environment, investors, founders and employees are seeking other ways to sell their stock.

SecondMarket has launched a private company marketplace to allow these shareholders to do just that.

The company, formerly known as Restricted Stock Partners, has signed up more than 600 potential buyers, who must be accredited investors.

SecondMarket, which raised an unspecified Series A from FirstMark Capital in 2007, enables shareholders to sell stock in two ways - in a one-off sale by a founder, employee or other stockholder, or in an organized sale with the company.

SecondMarket is emphasizing the latter option, where companies can create their own "micromarket," which will include only those that the start-ups allow in to the system. The company can allow specific buyers or a certain type of buyer.

The service, which has been in testing for about a year, was started due to the increasing interest from investors and employees from companies who wanted to unload their shares, said SecondMarket Chief Executive Barry Silbert.

"That IPO dream that seems to keep getting extended is now a non-issue because you can see tangible value in stock or options you own," Silbert said.

SecondMarket, which has about 100 employees, seeks to work with start-up companies, providing tools to manage custody of the shares, communicate with shareholders and keep track of other data. Start-ups can also control what information they provide to potential investors and choose different forms of sale such as auctions or static bid-ask sales.

During the beta testing the service has been mostly using common stock and options, which are often held by employees or founders, but Silbert said venture investors would benefit from it as well.

Asked why venture investors who already have secondary firms they deal with regularly would use SecondMarket's system to sell stock, Silbert said such investors could still benefit from finding new buyers that they did not know existed.

"We're seeing venture firms open to the idea," Silbert said. "Maybe they don't sell the whole stake but at least they're able to monetize a portion of their ownership."

The service also provides a more organized way with clearer information, Silbert added. For example, without the system, Silbert has seen examples of sellers calling five brokers to sell some stock. Each of those brokers would then call five funds, and people can soon end up thinking that 25 million shares are on the market.

"Most would agree that this is a more efficient way to do this," Silbert said.

Another firm, Millennium Technology Value Partners LP, also provides a service to start-ups through its "employee liquidity program" for start-up companies, in which Millennium buys stock from employees, VentureWire reported.