Hi Amy, I haven't heard anything back from Airbnb after reporting this guest. I made the report by going to his profile and scrolling to the bottom of the screen and there it says report this user.
As he had already left me a review, I then left a review saying what had happened which was that I woke up at 1am to find him lying at the end of my bed on the floor in his shorts and t shirt.
I still do not know the process around reporting someone. I can see that he is still using Airbnb.
Sorry to hear of your unpleasant experience.