Most commercial radio stations are owned by one of the major corporations (Clear Channel, etc). These big corps do not allow their affiliate stations play music which has not been approved at corp headquarters. Check with the local stations you want to get the song onto and find out what their submission policies are, then jump through their hoops.

As far as promoting your song to the public in general, your best bet is to perform it often and widely. Make a You Tube video and use Twitter and Facebook to direct viewers to the video. Try to encourage other performers to sing it. The bottom line is that it is very difficult to get a song out to large numbers of people. Persistence is necessary, as well as good luck.