How do you find beta testers? Any platforms you use?

My take on this would be to do things that don't scale. Reach out to your audience with a direct approach (which requires identifying which channels are best), and then maximize your efforts. For example on my end, I automated mass personalized DM on Linkedin using Walaaxy + Sales Navigator, then set up 30mn to 1hr video calls with each one that responded. I stopped when I got about 100 interviews done. Of course, this doesn't mean digital marketing must be avoided. For instance, I created a landing page and set up basic SEO things, + I wrote a few posts on other social platforms (Reddit etc.) to get backlinks on my domain, have natural traffic on my website, and additional feedback. Hope that helps.

I LinkedIn automation campaign with Phantombuster can work well. I usually run outreach campaigns to people active on the relevant hashtag and ask them for feedback. Contact request message: "Hi #firstName# I see that you are an influencer on the topic of #hashtag# and would like to connect" Followup message (when contact request accepted): "Hi #firstName# Thanks for accepting my contact request. I recently launched #productName#, I would be interested in your feedback, as you are an expert with #hashtag#" You can contact 100 people per week. 30 to 50% will give you feedback with this template.

https://betapage.co/ and https://betalist.com

You should check out Polywork! They just launched last week on product hunt and they're all about helping people find folks for things like this!

I happened to did just that with some success. I simply made a demo and asked on Twitter. Offered premium at launch.