After its triumphant debut on the stock market nearly two months ago, professional social networking site, LinkedIn, now has something else to brag about: it’s now the number two most trafficked social network in the U.S. in terms of unique visitors per month.

According to data released by comScore, traffic to LinkedIn grew 63% year over year(YOY) as of June 2011. Facebook, still by far the number social network site on the planet, experienced growth of 14% YOY. Twitter isn’t slowing down either, posting growth of 31% YOY. Tumblr had the strongest growth of all, tripling its unique visitor base up to 11 million, or 204% YOY.

How about Myspace, you ask? It continued taking sky diving lessons with traffic dipping 50% YOY. Good luck, Justin.