Here is an important question to consider.
Does the target audience you're trying to reach already interact with one another?
Do they know one another? Where and how do they interact?
The dream situation is an audience that knows each other, interacts frequently at events or via informal social situations, but has no central community they already participate in.
Here you already have a concept, you develop the platform, bring in existing offline discussions, create content about the members, and watch the community quickly come to life. The quickest successes, like Facebook, usually fall into this category.
More likely, you will have existing competition (existing communities) and need a refined, unique, community concept.
In both these situations, you're an enabler. The community exists and you're helping them be better at what they do.
If the audience doesn't already interact, you're a community builder.
This is far more difficult.
You need to individually reach out to people, make introductions and build strong relationships between them, breed familiarity, look for symbols you can embrace, gradually bring people into a platform, provide plenty of opportunities for members to take ownership over different areas of the community, identify the key topics they want to talk about it and repeatedly nudge members to do it.
If you're in the latter category, be prepared for a far longer and far harder struggle to get the community going.