If you didn't install any software like Prey to locate your stolen Mac then there really isn't much that can be done.
A MAC address can be connected with a serial number and computer id on Apple's records, and Apple could check their logs when said computer automatically contacts Apple for updates and other background checks like the time to get a idea what times the computer is used and at what IP addresses, this would take a few months. Only one time I've heard Apple actually assist in something like this and only because it was a celebrity.
The IP addresses can be generally located, more specific ones and the owners be found by the ISP records.
By the time your sure, get a court order and police to help, costs involved etc., pray it's still around locally and not several states or in another country...the effort involved...you could be spending more to recover it than buying a new one.
If your at a local college, you could ask the IT person to be on the lookout for the MAC address and who is logging in with it, also the local WIFI spots and such, try to determine a pattern.
You also could use KisMAC (enable Apple passive drive in preferences) and scan local free wifi spots and areas for your MAC address, try to locate the person with your machine.
Don't take action on your own, it's your word against theirs, rather consult with the police again as I'm sure you have already logged a criminal complaint right?