When I started trying to build the group in Frisco, I hadn't heard of AtheistNexus. My hunt for new blood was primary through a fairly popular community forum. I put out a post asking atheists (etc.) to give a show of hands if they were interested in doing a monthly meetup. I got a good number of responses but when it actually came time for people to get out of the house, nothing happened. I had asked for RSVPs and got a few "maybe"s. But no one showed up. It's pretty discouraging. The next time I tried, I was lucky enough to know another atheist who was interested in seeing a new group form. So the presence of another human made me much more willing to sit in a restaurant waiting for possible newbies.
About 2/3 of the people who have come to the meetings are from the local forum. The other third heard about us through AtheistNexus.
I tried to put a free ad into a local magazine, but they seem to have "lost" my entry. Once that ad goes through, I'll bet we get a huge burst of folks.