How to find your stolen mac on a network using the MAC address/Serial number
If they do come back to the same network and you just happen to be on and looking.

From the command line.

    arp -an


This will show you the IP and MAC addresses of any hosts active on the network at that time.

    $arp -an

    ? (10.0.1.1) at e4:ce:8f:68:85:c8 on en1 ifscope [ethernet]
    ? (10.0.1.13) at 0:19:7e:b0:37:ff on en1 ifscope [ethernet]
    ? (10.0.1.20) at 64:b9:e8:2b:ab:97 on en1 ifscope [ethernet]
    ? (10.0.1.28) at d8:30:62:76:ab:a0 on en1 ifscope [ethernet]
    ? (10.0.1.255) at ff:ff:ff:ff:ff:ff on en1 ifscope [ethernet]


This will at least tell you if your computer is back on the network. I doubt they would go through the trouble of spoofing the MAC address. 

Did you have Remote login turned on? If so and it shows on the network, you could login to your computer. This opens up more options.

Such as:

You could SSH into your computer.

Once in you could run something like this.

    while :  ; do sudo osascript -e "set Volume 10" &amp;&amp; say here i am &amp;&amp; sleep 30 ; done &amp;


Adjust "here i am" to what ever you want your Mac to say at full volume. I put a sleep 30 in to keep them from just powering it off right away and give you time to find them. It would probably take them a few times to figure out that it was the Mac talking. I'd scope out the Macs in the area before running it so I'd know where to look first.