I'll go back into some history...
March of 2008, I opened an Islamic forum. By June 2009, it had over 2000 members.
How many were active?
Less than 20.
So going back to the question... If you really want to make a website that will benefit the people, you have to create something unique. You have to attract the audience, without using a preaching fashion (in the lack of better words).
Alhamdulillah Masha'Allah, never for a split second have I regretted acquiring this forum. Members definitely play the biggest role. A forum, after all, is what it's members make it out to be.