Shameless plug for the service we built to solve this for ourselves - https://www.pickfu.com
The MVP was to meant to replace asking randos at a coffee shop about your idea/design/etc. Over time we've added demographic targeting, follow-up questions, and other requested features. Nowadays online sellers and other creators use it like an online focus group to validate ideas and products.
Some other ideas for finding an audience for your MVP:
- google the exact problem you're trying to solve, reach out to authors/bloggers who've written about it
- online ads to your target demographic
- LinkedIn prospecting (if you have a target customer profile)
- Subreddits of your target problem area
- Start writing/tweeting about the problem space and engage the audience that follows
- comments section of relevant YouTube videos