Well not really but several other people have asked me to help them with their groups too. I will try to post in your group when I can, but I think the best way to advertise your group is to advertise yourself.
I would say to spam a little in these groups and let people get to know you, and they will join:
BABA
Team neutral
Aperture Science
Team Rocket (be sure to tell BS I sent you - he is mad at me right now!:) )
Indigo League
The Pokemon Rangers
Team Magma
Team Creepy Hulk
The Happy Hut.
There are a core group of active people that are in all of these groups. They like to help each other out and generally will join the group of anyone who is active in these groups. Just be yourself, don't be too pushy or eager, but participate in the games. Maybe start a few spam games in your group so that people have a reason to visit your group besides just battling and when they need a battle they will remember your group.