You can't. The SN will only allow you to identify the iPod as yours if it is recovered.
- If you previously turned on FIndMyiPod on the iPod in Settings>iCloud and wifi is on and connected go to iCloud: Find My iPhone, sign in and go to FIndMyiPhone. If the iPod has been restored it will never show up.
- You can also wipe/erase the iPod and have to iPod play a sound via iCloud.
- Change the passwords for all accounts used on the iPod and report to police
- There is no way to prevent someone from restoring the iPod (it erases it) using it.
- Apple will do nothing