GWS:
Possibility exests that you have the right address- Papers arent considered served until the defendant identifies themself. Probably since you served his "buddy" he is expecting papers and has someone assisting him in dodging the subpoena.
Do you know what he looks like? There is of course a way you might be able to find out. If you can get a pic, its real easy to do some personal surveillance at that residence to see it he is entering or not (or pay a few hundred to a PI to check)- If he is and dodging the subpoena, its my understanding (from talking to a process server) that he is breaking the law (contrary to what you see on tv).
PM me what you have and I will snoop around- I use some more obscure search engines these days, which turn up different hits.
I have also pm'd you a link, to a public records db- that may help, with locating some other billings. If its all going to that address, most likely he is there. There are other sources to check as well if he runs a business-but lets wait on that.I have a couple other fish in the pan right now.
Scorp