The less successful teams in the English Premier League tend to not have many "plastic fans". Chances are if you support Sheffield United it's not because they went on a US/Asia summer tour, but rather because people in your immediate social environment (e.g. family and close friends) support them.
Actually, email matching might be suitable for this problem. I did a project for matching flatmates a while ago. [1] Was trying to leverage a user's facebook connections etc. to create better matches (e.g. 2nd degree connections).
If anyone is interested in taking it over/working on it let me know.
[1] http://www.flatmate.io/