Yes it has to on and connected to the internet
- 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.
- If not shown, then you will have to use the old fashioned way, like if you lost a wallet or purse.
- 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 without a court order
The SN will only help identify the iPod as yours if it recovered.
Unregistering will not have any real effect.
You can disassociate from your account since yo can only have 10 devices/computers associated with your ID