Among three leading social networking platforms—LinkedIn, Twitter, and Facebook—LinkedIn is the most effective source of leads for B2B companies, according to data from HubSpot.

In a study of 3,128 HubSpot B2B customers in 2011, LinkedIn generated a visitor-to-lead conversion rate of 2.60%, on average. That's four times higher than the average visitor-to-lead rate for Twitter (0.67%) and seven times higher than the average rate for Facebook (0.39%).

Moreover, LinkedIn is growing faster than Twitter and Facebook

Though LinkedIn now ranks behind Twitter and Facebook in monthly user activity, LinkedIn is growing at a much faster rate than both social networks, according to separate research from Compete.

LinkedIn attracted some 28.1 million unique visitors in March 2012, up 7.3% from 26.2 million in February, and up 60.7% from 17.5 million one year earlier.

By contrast, Twitter attracted 42.0 million unique visitors Twitter in March, up 35.5% from 31.0 million visitors a year earlier. Facebook attracted 169.9 million visitors in March, up 20.7% from 140.7 million a year earlier.

About the data: Findings are based on data from 3,128 B2B HubSpot customers that generated traffic and leads from social media in 2011, collected via the HubSpot system.