On the secondary stock trading market website SharesPost, Twitter has hit a $4 billion valuation. This is a $300 million increase in less than a month. In December, Twitter had a valuation of $3.7 billion. This trade is based on a smaller set of Twitter stock and it is not the official internal valuation. On SharesPost, Facebook’s valuation is trading at between a $50-$75 billion valuation.

LinkedIn has hit a $3 billion valuation in private funding in a recent trade on SharesPost. SharesPost sells shares of private companies as a secondary market. When SharesPost sold shares in LinkedIn at $30 per share, it gave the company a valuation of $2.91 billion. About 95,000 shares were sold at that price.

Secondary stock market service Sharespost has sold 165,000 shares of Facebook for $25 each. When you extrapolate this price across Facebook stock, it values the company at $56 billion. Sharespost said that the auction was “significantly oversubscribed.”

Social gaming company Zynga has hit a $5.51 billion valuation on SharesPost Inc. Given this valuation, it means that Zynga is essentially worth more than Electronic Arts. Electronic Arts is worth about $5.16 billion on the stock market.