The services Mister790 describes are likely your only hope, unfortunately. If you have any apps on your machine such as Skype or Yahoo messenger which auto-launch, and you can see that "you" are online from another computer, it may conceivably be possible to have authorities track this use down to the ISP, and then the ISP to the user, but it's a longshot.
Your computer in all likliness had a dynamic IP address (IP that changes constantly depending on where you are, etc.) Unless you had a statically fixed Internet-accessible IP address (such as you might have running a web server, etc.), there is not going to be a way to track it specifically by the IP.
Also, call the police, and definitely call Apple's Applecare line as well. They keep a stolen computer database, and if you have the serial number, they will enter it in, so that if the thief or a future owner of the computer takes it to an Apple store, it will set off a red flag. Similarly, if you are about to buy a computer on CraigsList, call the Applecare line and ask them to run the serial number and make sure it comes up clean. I buy a lot of computers, so I do this fairly often when I'm buying expensive machines that are high-risk.