LinkedIn has announced it has passed the 150 million member mark helping to seal its dominance over the professional social networking market. It passed the 100 million mark back in March 2011, but growth has been picking up steadily since then and it has added 20 million members since November.

LinkedIn released the 150 million figure as it revealed its latest numbers which has seen it double revenues for the fourth quarter with recruitment services being the fastest growing area of revenue by far.

Revenue for the fourth quarter hit $167.7m up by 105% compared to $81.7m last time. Net income was $6.9m up $1.6m.

For 2011 overall, revenue increased 115% to $522.2m while adjusted EBITDA increased to $98.7m from $48m last time.

Jeff Weiner, CEO of LinkedIn, said: “Q4 once again exceeded our expectations for member engagement and business growth. It was a fitting end to a memorable year in which we reinforced our position as the pre-eminent professional network on the web. We believe continued focus on our members and technology infrastructure positions us well for accelerated product innovation in 2012.”

Interesting to see where that revenue is coming from. It is, not much of a surprise, to learn that it is increasingly from recruitment advertising, which is rising faster than either online advertising or subscription revenues.

Revenue from recruitment products rose to $84.9 million in the fourth quarter, which was an increase of 136%. Recruitment revenue represented 50% of total revenue in the fourth quarter of 2011, compared to 44% in the fourth quarter of 2010.

Online ad revenue was also up, but the leap was not as large. Revenue from Marketing Solutions products totalled $49.5m, an increase of 77% compared to the fourth quarter of 2010. Marketing Solutions revenue represented 30% of total revenue in the fourth quarter of 2011.

Revenue from Premium Subscriptions products rose to $33m, which was an increase of 87% compared to the fourth quarter of 2010. Premium Subscriptions represented 20% of total revenue in the fourth quarter of 2011.

Revenue from the US was worth $112m, representing 67% of total revenue in the fourth quarter of 2011, while revenue from international markets hit $55.8m and represented 33% of total revenue in the fourth quarter of 2011.

Fourth Quarter Highlights and Strategic Announcements

• LinkedIn completed the latest phase of the re-architecture of its software development and deployment process, known internally as InVersion, which is the foundation for accelerated product innovation in 2012.
• LinkedIn continued its international expansion and localization with the addition of three new offices (Tokyo, Japan; Bangalore, India; and Sao Paulo, Brazil), and five new languages (Japanese, Swedish, Indonesian, Malay, and Korean.)
• At its Talent Connect conference in October, LinkedIn announced Talent Pipeline, a new solution that allows recruiters and hiring managers to manage, track, and stay in touch with active and passive candidates, regardless of source. Talent Pipeline is currently in pilot testing phase with select Hiring Solutions customers.
• LinkedIn unveiled two new offerings for Marketing Solutions customers at Connect:11 in October. Company Status Updates and the Certified Developer Program give brands more powerful ways to connect and engage with LinkedIn members.