With shares of Facebook recently hitting a $70 billion valuation in a private auction on SecondMarket , you'd think those are the only shares that trade on the private stock market Facebook did make up the biggest portion of trades (39%) in the fourth quarter of 2010, but the market for private shares is broad and demand is strong for all sort of shares from LinkedIn (7%) and Etsy (5%) to Chegg (2.5%)and Bloom Energy (2.5%). Last quarter, SecondMarket handled $158 million worth of private stock trades, a little more than double the $75 million worth in the third quarter. For the entire year, SecondMarket handled $400 million worth of private trades.