Forget online IMEI trackers — use the free, official tools already on your phone:

: An anti-theft app that provides advanced features like "fake shutdown" to keep the phone trackable even if a thief tries to turn it off. How to Find Your IMEI

You can find your IMEI by dialing *#06# on your phone, or looking at the original box.

Here is the harsh truth:

the device across all Australian networks (Telstra, Optus, TPG/Vodafone) so it cannot be used with any SIM card.