Facebook is a social networking service and website launched in February 2004, owned and operated by Facebook, Inc. As of May 2012, Facebook has over 900 million active users, more than half of them using Facebook on a mobile device. Users must register before using the site, after which they may create a personal profile, add other users as friends, and exchange messages, including automatic notifications when they update their profile.
you have to do manual search on facebook search box, as my research there is no outer option to find top groups to post ads on in Facebook.
Try insidefacebook you will find the information I think you need there. It lists top pages with most likes and activity Hope that helps
that's very pointless. The admin will simply remove the ads if you post directly and if you go through facebook ads i don't think they show up with private or public groups.