Sharespost, which tracks the valuation of venture backed private companies reports that Twitter's valuation is up 11.49% this week to $1.64 billion.

This follows Twitter's developer conference this week where it announced several revenue generating plans, such as advertising, and also said it would compete with some of its more successful developers.

Facebook is up 9% to $14.63 billion. Zynga, the maker of the popular Facebook game Farmville, is unchanged at $2.61 billion valuation.

Sharespost has created an index of the top venture backed private companies: Twitter, Facebook, Zynga, LinkedIn, Tesla Motors, Serious Materials, and Linden Lab. The combined value of the index is up 4%.

The valuation of companies in private markets is not an accurate measure because of the lack of liquidity in those markets.