On Thursday LinkedIn‘s stock more than doubled in its market debut due to investor demand for the social networking company to go public. The stock traded at $103 at midday under the symbol “LNKD” on the New York Stock Exchange. LinkedIn Corp.’s initial public offering on Wednesday night was priced at $45 per share, at the high end of the company’s initial target. The company raised $353 million in an IPO that valued it at $4.3 billion, the largest valuation for a U.S. Internet company since Google went public in 2004.

Founded in Mountain View, California on December 2002 by Reid Hoffman, Allen Blue, Jean-Luc Vaillant, Eric Ly, and Konstantin Guerickeand launched in May 2003, the free business social networking site allows registered users to create a professional profile visible to others. Through the site, individuals can then maintain a list of known business contacts, known as Connections. LinkedIn users can also invite anyone to join their list of connections. The company also offers free advertiser-supported services, in addition to premium services which cost from $5 to $200 per month. Job listings on LinkedIn costs $95. LinkedIn operates under the notion that people want to keep their professional networking separate from their personal social behaviors.

Linkedin reached profitability in 2006 when it claimed 5 million visitors. The site grew to 85 million members in October of 2010, and hit 90 million members when the company filed it’s S-1 to go public earlier this year. There were nearly two billion people searches on LinkedIn in 2010.

LinkedIn’s site is currently used in over 200 countries and territories around the world, with more than half of LinkedIn’s users coming from outside of the U.S. (44 million in the U.S., 56 million outside of the U.S.) LinkedIn is currently available in six languages: English, French, German, Italian, Portuguese and Spanish. LinkedIn’s fastest-growing country is Brazil, with 428% growth year-over-year. Brazil is followed by Mexico (178% year-over-year), India and France.

Currently 17.8 million LinkedIn users are members of the network’s Groups and 1.2 million post comments to Groups weekly. There are now over 2 million company pages, with eBay, Amazon, Apple, Cisco, EMC and Campbells as the most represented companies on the network based on the number of employees that are on LinkedIn. There are now 1.3+ billion connections between LinkedIn’s members and 79+ million job transitions/changes tracked on the network. As of January 2011, LinkedIn counts executives from all 2010 Fortune 500 companies as members; its hiring solutions were used by 69 of the Fortune 100 companies as of December 31, 2010.

Currently Headquartered in Mountain View, LinkedIn also has U.S. offices in San Francisco, Chicago, New York and Omaha, Neb. International LinkedIn offices are located in Amsterdam, Dublin, London, Paris, Sydney, Toronto and Mumbai, India. LinkedIn started off 2011 with about 1,000 full-time employees located all around the globe, up from around 500 at the beginning of 2010. The Company’s valuation is estimated to be nearing 3 billion dollars.