Finding & retaining early beta testers

Hi Product Hunt folks, I'm working at an early stage mental wellness startup and we're in the process of testing the early beta version (more like an alpha, really) of our app. I'm relatively new to product marketing and am looking to harness the wisdom of crowds here. I have two questions I'm hoping the community can comment on: How do you generate leads for beta testers who aren't friends and family? How do you retain these folks once they've opted in? Here's what we're doing: Currently, our strategy is to use a service like mTurk to perform customer discovery and refine our product-market fit. A nice bonus is that we'll ask these folks whether they're interested in testing our product. This has led to decent conversion into beta testers. Beyond that, we have a signup form on our site where people who find us organically can opt-in if they're interested. As far as retaining these folks after they've tried out our app, we are trying to figure out the best way to do this. We're currently offering to push all future updates to our beta and let them continue using the app until our public launch. But beyond that, we don't really have a place for these folks to interact or ask questions. Has anyone found a good solution here? Start a Slack channel for beta testers? A forum? Or maybe just have them follow you on Twitter? Thanks in advance for any advice! Zach