I have seen hosts and guests asking questions how to get hold with Airbnb support. It is very frustrating when you find it is hard to find contact information. Here are the steps for you to get contact with Airbnb support either by phone or by messages through Airbnb mobile app.
(1) Profile->Get Help
(2) Scroll all the way down and press Contact Us button
(3) Press It is something else
(4) Press message us to start a message to Airbnb
Or press Call Us to get the phone numbers. The toll-free number is free to call in US and Canada
If you want the message to be specific for a reservation, on step 3, as a host you press Reservation->Home hosting->pick a listing->Press Past->choose the guest reservation->press Something else. As a guest, press Reservation->Traveling->Something else