According to a new study at University of Massachusetts at Dartmouth, LinkedIn is currently the most used social media tool among the fastest-growing private companies.

In this study for the Center of Marketing Research, 81% of companies listed on the 2012 Inc. 500 (the fastest growing companies) use LinkedIn, up from 73% a year earlier. Meanwhile, the number of these companies using Facebook has actually declined to 67%. Twitter use is currently tied with Facebook, up from 64% in 2011. Foursquare, YouTube, and Pinterest lag behind, with a stalwart group of 8% who still refuse to get on the internet, dammit.

A majority of companies believe that social media is necessary. However, social media growth might plateau; 44% plan to spend more on social media this year, down from 71% who planed to increase spending in 2011.

This study was based on a nationwide phone survey of the companies named by Inc. Magazine to the 2012 Inc. 500 list (top ranked out of their 5000 list). 34% of these companies participated in the surveys.

Also, on a slightly different note: those emails LinkedIn sends about who has looked at your profile! So stupidly fascinating. Keep doing that.

[Marketing Profs, image via Getty]