How can I get people to join my facebook group?

[Madsummer967]

When your friends join a group, you are likely to get a notification about it, especially if more than one joined.
It is also likely that you will get it requested, on the right hand side of your page, where random people and groups show up. No one physically requested you see it, but if enough of your friends are part of a certain group, it may be suggested to you.
Also, you can invite friends to groups. You can invite your entire friends list to every group if you want.

And that's how most groups get popular. Not by each individual searching for the group, but by people suggesting it and showing it to you.