Last week, the business professionals’ social networking website, LinkedIn reached the milestone of 100 million users; and is reportedly growing at a rate of one million new members every week.

After launching in 2003, the social media platform has steadily developed into a huge online community where like-minded people can network, seeking jobs and new business opportunities. And with an increasing number of features such as LinkedIn Answers and groups, it is easy to see why it has become popular amongst B2B marketers.

As you would expect, the news of LinkedIn reaching this milestone has drawn many comparisons with the social media behemoth that is Facebook, with most commenters citing that LinkedIn still has some catching up to do to match the 600 million or so members currently on Facebook. That might be the case on a pure numbers basis, but if we are talking about return on investment and influence from a marketing perspective, then arguably the greater gains are to be found on LinkedIn when you consider the demographics of a typical user. With Facebook’s business model primarily targeting social interaction, it tends to attract huge numbers of school and college students, whereas LinkedIn is much more focused around the business community, and arguably individuals with greater spending power.

This could be the very reason that Facebook has begun introducing more business-oriented features including Facebook Pages and more recently, Business Pages. All interesting developments which raise the question about which platform is better for marketing your business online – Facebook or LinkedIn?

Which one would you choose?