Hi Molly, something very similar is happening to me, too, I just posted about it. In addition to feeling terrified, we are incurring fines due to his illegal activity, and Airbnb hasn't done anything about it. I've dedicated every ounce of my free time to speak with Airbnb, only to be disconnected, rerouted, and ultimately dismissed. Airbnb should pay my fines. All Airbnb needs to do is ACT and remove the ILLEGAL listing.
My only advice (so far) is to contact your local city council or district attorney's office, and potentially the police. Please feel free to tag me with your progress. I wish you the best of luck, truly. You're not alone and I'm so sorry this is happening to you. Nobody deserves this.