I get asked this question all the time. I just read this article on Mashable.  Thought you might find it and the very cool/detailed infographic interesting and helpful.

“In answer to the question above, approximately 18,400,000 Americans say yes, they got their current job through Facebook. Though Zuck’s platform ranks #1, Twitter and LinkedIn don’t have shabby numbers either — 8 million and 10.2 million Americans, respectively, have gotten their jobs through social platforms….”
read the rest here.