As several Internet companies like business networking site LinkedIn and Russian search giant Yandex have successfully sold shares to the public, according to reports, Zynga Inc., the biggest maker of games on Facebook, is expected file for an initial public offering by the end of June.

The recent IPOs of several Internet companies show huge investor demand for fast-growing and high-profile social media Internet firms. For instance, LinkedIn had its IPO last week and saw its market valuation at $9 billion, which is twice its pre-IPO price.

Pandora Media Inc., a music-streaming service; HomeAway Inc., an online vacation- rental site; and Cloudary Corp., a Chinese Internet company, have already announced plans to go public. Also expected to go public soon is social networking giant Facebook, which has a value of $55 billion, according to SharesPost Inc., an exchange for private companies. Twitter Inc. is also expected to go public in coming months.

Zynga's IPO this month is expected to be successful given its rapid growth and successful game launches. Zynga has created some of the most successful Facebook games, including Farmville, Mafia Wars, Texas Hold Em, Petville, Cafe World and Scramble. Zynga has something for everyone: casino games, word games, board games, role playing games and party games which can be found on Facebook, MySpace, Bebo, Friendster, and Hi5. Zynga games have 235 million monthly active users across social network and mobile platforms. It has six times more users than the second-leading developer, Mensing, creator of Madden NFL and Pogo Games Fanatic. Zynga makes money by selling virtual goods within the apps and letting players pay to reach higher levels.

Zynga has an $8.2 billion valuation on SharesPost. Electronic Arts Inc., which is the third most popular game developer in the Facebook platform, is valued at $7.71 billion on that Nasdaq Stock Market.

The privately held four-year-old firm Zynga's stockholders include venture firms Foundry Group, Union Square Ventures, Kleiner Perkins, Institutional Venture Partners, Andreessen Horowitz, Digital Sky Technologies, and Google Inc.