Grow your Facebook group with ads. One of the easiest ways you can get people to join your group is to run some targeted Facebook Ads. Like I mentioned before, running ads requires a page. Once you’re happy with how your Facebook group and page look, head over to Facebook’s Ads Manager. Click on the green Create Ad button in the top right.
https://neilpatel.com/blog/an-eye-opening-guide-on-how-to-grow-a-facebook-group/