I have booked (and received a confirmation) from my host, but now when I am trying to send them a message, I get a warning saying that this host has not yet verified their account so I can't contact them.
I'm sorry to hear that you are having such an unsual experience with your host. I would get in touch with Airbnb via Twitter @Airbnbhelp. Have your reservation details handy. They will ask you to send them a PM with your reservation details. Never share any person details in your public tweets. Do mention that you are concerned that you cannot get a hold of your host and verification are still pending. They will definitely be able to shed some light on the matter. Also, if you are not confortable, I would ask if you can be re-housed with another host. Cancelling on your end will dock your user fee which is non-refundable, so get in touch with Airbnb first.