Like other hot startups there is a healthy secondary market ecosystem for Twitter stock. The current street value of a share of any series of Twitter stock At least $7 per share, say multiple sources with knowledge of transactions. With 225 million shares outstanding after a three for one stock split earlier this year, that&'s a $1.575 billion valuation.

There aren&'t nearly as many early Twitter employees with sizable amounts of stock to sell compared to Facebook, but the demand is there for those that are in the market. There are even a few funds that have been created with the sole purpose of buying stock from Twitter employees and investors, and the Twitter board of directors generally doesn&'t interfere by exercising its right of first refusal.

The $7/share valuation is generally considered the &''fair&'' price for larger transactions of at least $1 million. Smaller transactions, which can attract a more robust number of potential buyers, are sometimes closing at higher valuations, we&'ve heard.

Twitter was last officially valued at $1.1 billion post money when it raised $100 million late last year. The company is still effectively revenue-free.