Between the three, Facebook is literally everyone I've ever shaken hands with at a conference or kissed on the cheek at Easter. Twitter seems to be everyone I am entertained by or I wish to meet some day. Foursquare seems to be everyone I run into on a regular basis. All three of those social graphs are powerful in their own.
Dennis Crowley is a successful businessman known for his contributions to the technology and startup industry. He might be associated with founding or leading prominent companies.