Yesterday in the social network LinkedIn’s blog an article was published to announce the achievement of the 100 million users threshold.

LinkedIn is the largest professional social network in the world. It was founded in December 2002 and launched in May 2003. Over the years it received several investments for a total of over $100 million and in 2006 it started having profits from advertising and the sale of Premium services.

LinkedIn users reached 50 million in 2009, after nearly six years after its launch, so it took only one quarter of that time to add 50 more million, a sign of this social network’s success. To give an idea about the other major professional social networks, Viadeo has about 35 million users and Xing has about 10 million users.

Nearly half of LinkedIn users are from the USA, over 20 million are Europeans of which approximately 5 million Britons. India has about 9 million users. Currently however the major expansion is taking place in Brazil and Mexico.

Of these 100 million users of course not all are active. Inevitably many registered years ago and for various reasons are no longer interested in using LinkedIn, others have signed up because at one point it seemed to become almost a fashion among professional users but then they haven’t really used this social network. It takes some time to figure out the best way to use LinkedIn’s services, also because different users may have different needs. Essentially you have to invest some time to learn how to use this tool.

LinkedIn offers many free services that allow job search and offering but also the opportunity to get in touch with other companies and professionals to do business together or just to exchange opinions and information.

To enrich you profile a variety of applications are offered allowing for example to include the latest excerpts from your blog, to share titles of books read or to insert presentations in various formats.

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As in any social network, all users can build their own network of connections. LinkedIn recommends to add to your network only people you know, however some users adhere to the LION – LinkedIn Open Networker – philosophy, based on the belief that every person included in your professional network is an opportunity. Basically the idea is that a person that today is a stranger tomorrow could become a business partner or introduce us to one who is part of his professional network. The LION adopts a philosophy in the Open, Random and Supportive style typical of Ecademy, another professional social network smaller than LinkedIn but very dynamic because contacts are chaotic and can lead to unexpected opportunities.

For the record, personally I’m an open networker, so if anyone wants to join my professional network on LinkedIn you can ask me to connect and I’ll be happy to welcome you.

Among the possibilities provided by LinkedIn to virtually meet other users there are mainly the groups. In most cases group topics concern business but there are also some dedicated to sports and other entertaining subjects such as science fiction. There are many national or even regional groups to allow those who work in a geographically restricted field to find companies and professionals in their area more easily.

LinkedIn also includes a section devoted to questions and answers in which anyone can ask a question and / or answer those posed by other users. The user who asks a question can choose the best answer and the answers that can be considered good so with your answers you can increase your visibility, especially answering questions concerning your line of work.

The people who use LinkedIn services a lot can subscribe to its Premium services: there are different levels and dpending on how much you’re willing to pay you can have progressively more complete information about users in the searches and greater visibility in job search and offering. However it’s a voluntary choice as LinkedIn free services are adequate for most users.

At the end of January 2011 LinkedIn started the procedures for and IPO with the hope of selling shares for $175 million. This only gives a partial idea of the value of a social network that is now the most important for professional users on the Internet.