3.LinkedIn

LinkedIn

LinkedIn is a business-related social networking site. Founded in December 2002 and launched in May 2003, it is mainly used for professional networking. As of 4 August 2011, LinkedIn reports more than 120 million registered users in more than 200 countries and territories. The site is available in English, French, German, Italian, Portuguese, Spanish, Romanian, Russian, Turkish and Japanese. Quantcast reports LinkedIn has 21.4 million monthly unique U.S. visitors and 47.6 million globally. In June 2011, LinkedIn had 33.9 million unique visitors, up 63 percent from a year earlier and surpassing My Space. LinkedIn filed for an initial public offering in January 2011 and traded its first shares on May 19, 2011, under the NYSE symbol "LNKD".