Brian,
I invited several people and I think except for one or two, all of them joined.
Yes sending around PMs is a good idea, however I think we should be careful and send them to only members we are familiar with so people don't start accusing us of spamming.
Another idea is to watch out for classified ads that are about to get pulled (non radio related items) and message that member about this place and how he can list them here instead. I saw a couple of those but missed the chance to send a PM. Also I personally have put the link in my signature, if some of you don't mind you could also do that.
I was also thinking of maybe even buying some ad space from Alan on the forum if it's not too expensive. But that will probably have to wait a little while.
-Carlos