The YEC is a great option: http://yec.co/ I'm a member and have gotten a lot of really solid connections, intros and press out of it.

You'll want to get the right names in there first to make it more compelling to people. Offer free membership to influencers that your potential customers want access to or look up to. You may also want to offer a steep discount or free membership to existing members and just start charging future members. This way your existing members feel special, they'll keep the community active and future members will get more value for their money since there's already an active community going on. There are a lot of other little tricks and things you can do to get the community started on the right foot, but those are two simple things you can consider starting with.