Pretty much what blueloo said, but personally I would get on to the Gold Coast coppers first and report it stolen. They may not care very much but that's their problem.
Then I would call the airport operator to advise them that the bag had been stolen from the security point and that I was talking to the police about it. I'd then tell them my next call was to the Gold Coast Bulletin
. I assume from your location that you're a local in which case you may be able to make more effective waves than your friend, if she's an out-of-towner. This shouldn't be the case but it often is.
Generally the airport operator is responsible for employing security staff and maintaining the screening points (apart from the big airline-operated terminals in the capital cities where the airline administers the contract). I wouldn't even bother talking to the screening company but would go straight to the airport operator. I would also complain about the demeanour of the staff present at the time if they didn't assist. Gold Coast Airport is international with a small AFP/AUP presence and they should have been called (it's not like they're very busy
).
There may or may not be decent CCTV (airports are pretty variable in this regard and even the best system can bug out at times) and they may or may not want to show it to you. The threat of bad publicity may help in this regard.
Did your friend have travel insurance? If so it may help to get them involved as well. Good luck!