Airbnb guest stole my bag!!

I rented out a room in a large house advertised on AirBNB and there were 3 other guests staying there at the same time, as well as the host.
Everyone seemed like nice enough people and I felt pretty comfortable. I decided to pop down to the shop to grab some groceries and when I came back about an hour later my bag was gone. And I don’t mean a small bag. It was all my belongings I had brought with me. The host informed me that one of the guests had just left but she didn’t notice what bags they had with them.
We both spoke to AirBNB when I called to report it, and both of us got the same generic answer that without proof their hands are tied. What proof could I possibly have? A note from the thieves saying “Sorry, I stole your bag”?
The host was shocked but she was really lovely and helpful with the whole situation. AirBNB on the other hand are the scum of the earth as far as I’m concerned.