There are many methods to join automatically member on your facebook group. A tool that I often use is Fplus, it will help you to search through UID. Especially, it is quite useful with many guest functions such as posting, sending messages, sharing, commenting ... Or you can use the website griper (dot) net to search for groups quickly then get members in those groups. That will reach people more effectively
I think you can use Fplus which have many functions such as: sending message, sharing, posting, joning group....This tool will help you in avoiding facebook which detects your action and can flexibly change your content. But it doesn't give really accurate results, you can click on griper (dot) net to find active facebook groups and join them faster.
