When you’re starting a niche social networking site, getting your first 2,000 members is a crucial step. And the more members you can get before you even launch, the better.

Apart from tapping into your existing networks and connections related to your niche, offering early-adopter invitations while still in beta is a great idea. Not only does this give you early users, but limited invites can actually create some buzz around your launch.

Now a new web service lets you create a viral “Launching Soon” page for your social network to start building your pre-launch list.

LaunchRock collects user emails with the offer to let them know when your site launches.

That’s pretty straight forward. A simple opt-in form could do the same thing.

Where LaunchRock, well, rocks is that when users submit their email address, it invites them to use share buttons (Facebook, Twitter, or email) to invite their friends.

“The more friends you invite, the sooner you’ll get access!” is the proposition…

The brilliant thing is that this lets you tap into your potential members’ social networks before you even launch!

With the right site and supporting copy, this could be a powerful tool to get potential users to share the link to your site before you even launch.

It shows returning visitors how many visits and sign-ups their links has generated.

The LaunchRock blog has some good tips and case studies, as well, and gives full credit for the idea to Forkly.