Remember that there is Art for each START.
3 Things you should think of before creating your online community platform:

Find the most passionate and influencer persons within your niched community, talk with them.
Write down all features that drive a real time and live active community.
Keep on offering freebies to your communities (think of all kind of freebies).

After all, it is not a php or java developer that can make a community but he can support it and it is the social and local aspect that has to dominate in each community profile.

Use all vertical marketing channels from video, bonuses, mobile, and International e-events.

Guy Kawasaki The Art of the Start.

10-20-30 Rule