@Abigail3I have encountered guests like this as well. Some people may not have Airbnb app on their smart phone and may not check email carefully. You may try all possible communication ways:
(1) Airbnb message
(2) Text message by getting the guest's phone number from Airbnb app. The phone number shows up because it is a confirmed booking.
(3) Calling the phone number on Airbnb app.
You may want to consider to have a lockbox or a digital lock on your door. Then you don't have to wait for a guest's arrival.
You may also write a checkin and checkout time in your House Rule section. And warn guest that a non-responsive guest about checkin and checkout time may result in a cancellation of the reservation.