The concept is not entirely new. Nyppex, formed in 1998, facilitates private-company stock trades, and a few companies with similar offerings emerged during the last economic downturn but failed to gather much steam. Among the problems: Determining a fair price for a private company’s stock is tough without much public information. And while these services may be able to speed up dealmaking, users must still grapple with another key issue: how to determine a fair price for stock in a company that isn’t required to regularly disclose its financial information and doesn’t have that many potential buyers or sellers.

Still, some buyers, sellers and startups may see trading through these services as the way to go until the IPO market improves. “At the very least, it’s going to be spring training for companies before they go public,” SecondMarket’s Barry Silbert said.