Every time I turn on the hot water from faucet and shower in upstairs bathroom, I hear a dripping sound. The result is hole in my first floor ceiling.

The leak is not between the ceiling and the shower above.

If this only occurs when hot valve is opened the leak will be at the valve stem on the hot side of the shower valve. If the dripping occurs when either the hot or the cold is opened the leak may be at the shower valve or it may be at the shower head.

I agree, remove the escutcheon plate and handle. Look inside with a flashlight and see if the underside of the valve is wet. This could be the valve itself or the pipe running up to the shower arm.