Do you get 0 fans on all matches, or just friendlies? Most likely is a ticket price problem, and friendlies must have a way lower ticket price.
For an example, i have league matches with a ticket price of 9, and always get full attendance. In friendly matches i only get 20k/23,5k, with price 2 tickets.

If you have 0 attendance at league matches, either you have a way too high ticket price, or are doing really really badly in the league (this also decreases attendance) or there's some sort of bug :P