If you follow a sensible community development process, it should be impossible to launch a community platform that no-one joins.
There shouldn't be a breath-holding moment whilst you wait and see if people will register. You shouldn’t launch a site until you have 50 to 100 members that are going to use it. That means you have built up a list of 50 to 100 people whom you have personally interacted with. You have probably introduced them to each other on a simply mailing list or Facebook group.
If you don’t already have contacts before you begin, you need to identify your target audience, introduce yourself, find out how you can help them, ask them what they want and then offer them what they want. Introduce them to each other and start a few initial discussions between them.
This is hard, sure, but it's also very important work to get the community started. Once you have your first 50 – 100 members, you can begin steady growth and keeping them active and engaged.
But you should never have to worry about launching a community which no-one joins. If you can’t get 50 to 100 people excited and interested about the community, then don’t launch one.