I created a group for Planetarion on Steam.
http://steamcommunity.com/groups/planetarion
Join it with your Steam account (if you have one) and invite everyone you know you play CS / CS:S / TF2 with. Might help to spread the Planetarion word a little :-)
Apologies for the immensely crap graphic. I'm yet to find a PA related one that fits, as it has to be square so all the current ones are to wide & look even worse squashed up.