You can look at the members in this group, they are people interested in beta testing.
You can see if they've recently been active on the forums and then send them a PM offering. Or let the group leader know and he can post in the group about your opportunity.
Also, if you are in the "Private Developers Group" you can check out this thread: http://forums.toucharcade.com/showthread.php?t=55229
, if not, you can apply here: http://forums.toucharcade.com/profil...editusergroups
And a lot of developers post in the "upcoming games" forum saying they need testers and how to apply.