Your community effort will struggle if there isn’t some form of loose connections between the people you’re trying to reach. How else will members tell each other about your community?
Research informal connections before you start. How do your audience currently communicate with each other? Do they talk at the office? Do they have regular offline meetings? Is there a mailing list? Do people talk simple to their through e-mail contacts?
When you have this information you can be aim to be in those places and amplify those existing connections.You can reach groups of people at a time and help them bring their own network in. It’s far easier than inviting every individual at a time.