Bugger! I really hate low-life scumbags that steal personal property. What they need is is to be caught by the bike owner and dealt a bit of rough justice.
I guess there's a chance you could get the bike back since it's not something they can sell without attracting attention.
Penalties for that sort of thing aren't severe enough in Australia. If they get caught they'll probably only get a stern talking to by a magistrate and have to pay a paltry fine. They don't generally have to compensate the owner for their loss. I know that from personal experience when a couple of thieving cunts broke into my garage and stole helmets, a chainsaw and other tools worth a couple of thousand bucks, most of which wasn't recovered. At least they didn't get any of my bikes, which were secured with disk locks. They were stupid enough to get caught by the cops while doing another burglary later the same day. For their several burglaries including mine, they each got a $100 fine and no jail time. The most severe punishment was having to endure a lecture from the judge who told them not to be naughty boys again. In his summing up he said the offence was "out of character" for the otherwise decent young men. WTF? They both had rap sheets as long as your arm! I was $500 out of pocket for the insurance excess, which they weren't required by the court to compensate me for. How is that justice?
A few months later the same pair of youths were caught doing an armed robbery with a sawn-off shotgun. Out of character my arse! It's a lifestyle for those pricks, not a one-off error of judgement. They actually did time in the big house for that little error of judgement.
I'm in a particularly uncharitable mood at present because my elder sister had her car stolen yesterday. It was just a little old Mazda, not worth much because she's a pensioner who can't afford a fancy car, but it was a her only means of independent transport. She's living in temporary rented accommodation without garage parking because her home was destroyed by fire a while back (not her fault, but that's another saga). Talk about kicking someone when they're down. Probably a good thing that I don't know who the bastards are or I'd most likely be facing an assault with GBH charge by now.