Does Find My Mac stop working after the system has been wiped?
If the thief just wipes the harddrive, there is a slight chance that your device will still show up in Find My Mac as the association is saved in the NVRAM which persists even after a drive format.

However, if the thief or new owner clears the NVRAM in any way, or reconfigures iCloud with another account and enables Find My Mac for it, the association will be deleted or overwritten, and you will no longer be able to track your device.

See this question for more on the subject.