Three things to check:
1. What do your by-laws say about short-term letting?
2. What is the council zoning for your building – e.g. is it permanent residential?
3. Do you have irrefutable evidence of what is going on and are other owners prepared to do what is necessary to stop it? Bear in mind, by the way, that some might think this is a great way to make money out of their units.
If short-term lets are banned by your by-laws, issue a Notice To Comply. Also, contact airBnb and tell them that this owner is in breach of THEIR rules and has misled them by ticking the box that says he has permission to let the flat. Ask them to take the listing down.
If council zoning forbids short term lets, contact them with a complaint and ask them to send a “cease and desist” letter to your neighbour.
If you have a majority of owners on side, pass a by-law to tighten up restrictions of short term lets and then pursue them with everything you’ve got.
Regardless of what agency they use, this short-term letting disease will only spread if you don’t snuff it out now, eventually your other owners will take the view “if you can’t beat them, join them”.