I did a little research looking for the top 10 teams with most fans in FootyRoom and I gotta say im a little surprised. 

1- Manchester United  3543 

2- Chelsea  2045

3- Barcelona  1644

4- Arsenal  1517

5- Real Madrid  1406

6- Liverpool  1164

7- AC Milan  398

8- Manchester City  376

9- Juventus  276

10-  Bayern Munich  195

Looks like there's a lot of English fans here. ;)

Lots of United fans obviously...

Looks like it matches up fairly closely with the worldwide figures, in COYS' thread.

Those are just registered users though...