I remember when I first opened my forum it was both to make money but then eventually converted to just wanting a cool community, boy was it rough. I tried everything from hiring posters to talking to myself and even having contests just to motivate people. I got so desperate I started the "Get paid to post" campaign and even then people didn't become active! Finally I found the thing that generated active members it was unique content. Depending on your niche it's actually easy just make something that no one else has and they'll come to you. In my case it was the video game niche and I paid a programmer to make a simple tool for a game called world of warcraft and my forum got filled with leechers which then converted to members =) hope this helps