Are you sure Facebook and Reddit are the best ways to go for an MVP test? Reddit requires time and subtle messaging, Facebook is good but you need to be in the right groups and build a good messaging in order to succeed. In my experience, the best way is to offer something to the ones who'd like to test and give feedback. Don't go for Ads before testing first! You might be wasting your time, money and product reputation.

Please let me know if you need some help.