Tomato frogs will bury themselves if they feel uncomfortable for the first few days they are acquired.
My Tomato frog Bob buried himself so well the first day i got him i thought he escaped! But tomato frogs
wont bury as often once they have acclimated into their new environment. But if he isnt hiding, provide areas he
can bury under like some cork or half logs. But it could be very serious if there is no progress.

What are the dimensions of the tank? temps? humidity? etc...