Facebook, and Zuckerberg, embark on mega-IPO SAN FRANCISCO (Reuters) - Facebook took the first step toward public markets in the year's most highly anticipated IPO, which could catapult co-founder Mark Zuckerberg into sixth place among the world's richest people. The world's largest social network, a dorm room project for Harvard dropout Mark Zuckerberg that exploded in popularity and vaulted to Silicon Valley's top tier within 8 years, is expected to make its market debut in the middle of the year. It could raise much more than the $5 billion initially targeted, and value Facebook at up to $100 billion. The company, which some investors fear may have peaked in terms of growth, now has 845 million users. Revenue in 2011 was $3.71 billion, up 88 percent from the previous year but at the low end of expectations. Net income rose 65 percent to $1 billion. The long-awaited filing on Wednesday for an initial public offering kicks off a months-long process that will culminate in Silicon Valley's biggest coming-out party since the heyday of the dotcom boom and bust. Facebook appointed Morgan Stanley, Goldman Sachs and JPMorgan its lead underwriters. Zuckerberg's 1.11 billion Facebook shares are worth about $33 billion, based on a per-share value of $29.76 that the company assigned to its restricted stock units on December 31. Overview of the company: link.reuters.com/rev36s User growth over the years: link.reuters.com/mut36s Bankers fees -- how low? link.reuters.com/fep36s Top 10 global IPOs: link.reuters.com/myn36s The Zynga factor: link.reuters.com/paf65s The $5 billion figure in Wednesday's prospectus was an initial figure and could change based on investor demand. The prospectus underscored how 85 percent of Facebook's 2011 revenue was derived from advertising. Last year, social-gaming company Zynga, creator of Farmville, accounted for 12 percent of Facebook's revenue. The company Zuckerberg started in his Harvard dorm room in 2004 that grew into a global phenomenon dwarfs any recent Internet debut, such as Zynga, LinkedIn Corp, Groupon Inc and Pandora Media Inc. Their IPOs had mixed receptions. Google raised just shy of $2 billion in 2004, while the more recent Groupon scared up $700 million and Zynga managed $1 billion. Facebook's growing popularity among consumers and advertisers has pressured entrenched Internet companies such as Yahoo and Google. In 2011, Facebook overtook Yahoo to become the top provider of online display ads in the United States by revenue, according to industry research firm eMarketer. "Zuckerberg is trying to send a bona fides message to techies and users," said Max Wolff, chief economic and senior analyst at GreenCrest Capital. Very smart and under the radar.