Advertising on forums can be a double edged sword. Once you get yourself a good number of users who are also heavy posters on a forum, word of mouth advertising alone is going to keep on building your numbers. However, you need to be aware that the same forum they use to praise, they use to complain, and many of the little mistakes your employees might do, can end up published as new threads on the forum. With the right approach the damage can be mitigated, but you really need to have a good service to keep such threads to a minimum.