Here we go...
If you were ticketed (and your bags tagged) LHR-HKG-SYD (or wherever it was in oz that you landed) then it is the responsibility of the last carrier travelled to take the report and find the bag for you. If however you only flew LHR-HKG with BA and not gone any further on that day then you should have made a report with their ground staff in HKG. HOWEVER....As a member of the Oneworld Alliance Qantas should be able to help you either way. They may not be able to play around with your report on Worldtracer but they should at least give you some info on the status of your luggage.
Best of luck with it. I am a former baggage tracer and Im sure they will turn up soon.