Abstract
To reach 50 million users, it took thirty-eight years on the radio, thirteen to television, internet four years ... while Facebook has won 100 million members in less than 9 months. (Balagué et al., 2010). Today, this social network has more users that there are people in the European Union (Zuckerberg, 2010). As for latest fads in social networks, Twitter has allowed its 145 million Internet users (Williams, 2010) to send more than two billion "Tweets" in 2010(Costolo, 2010).Appeared in the early 2000s with My space, social networks are experiencing a exponential growth of Internet. According to a study by the usage of Internet, published in August 2010, more than 20 million Internet users would have enrolled on a community site and more than 8 million would make it there every day (Médiamétrie, 2010).
With Internet becoming more and platforms that are constantly increase, social networks appear more like media essential for brands. In this context, it is not uncommon for brands significantly change their comprehensive communication strategy, often at the expense of traditional media. This was the case of Pepsi for the first time in 23 years, decided to abandon its traditional commercials during the Super bowl in 2010, to spend the 20 million dollars that cost him such a unique campaign ads on social networks: The Pespi Refresh Project, which provides among other financing projects or individual citizens collective. This decision reflects the current trend of brands to lose interest traditional media to turn to new media, such as networks social (Pellicer, 2010, p.30).However, brands are still struggling today to analyze opportunities offered by social networks in the long term (Smith, 2009), and in most cases they not know how
