Zynga shares spike on Facebook IPO

Mark Zuckerberg and his $28 billion-in-waiting aside, one of the biggest winners thus far from Facebook's initial public offering announcement is Zynga. Shares in the company have spiked 33 percent since rumblings of Facebook's imminent IPO filing emerged on Monday. The CityVille creator is currently trading up nearly 10 percent to $13.60 per share as of press time.

Prior to this week, Zynga's stock valuation has floundered since its own heavily hyped IPO in December. The stock came out behind on its first day of public trading, after the company set an opening valuation of $10. Since then, the stock hadn't shown much signs of life, bottoming out at $7.97 per share in mid-January.

However, as revealed in Facebook's Securities and Exchange Commission filing, Zynga is a significant contributor to the social network's top line. Of the $3.71 billion in revenues Facebook earned in 2011, 12 percent, or about $450 million, came from Zynga's sale of virtual goods.

Zynga products account for seven of the top 10 games on Facebook, according to AppData.com. Currently, Zynga's CityVille, Texas HoldEm Poker, and CastleVille are the top social games on Facebook.