Cats are creatures of habit and do not like change. Mo is scare, which is very normal.

If you can, isolate Mo in a spare room with his litterbox, food and water, a radio playing soft, quiet music and some toys.

Go into the room and sit on the floor with some treats. If you keep doing this, he will come out eventually, once he feels comfortable.

If you can't isolate him, then just let him come out at his own pace. Don't try to pull him out or force him in anyway to come out. That will only enforce his being scared. You need to take baby steps. It's going to take time, love and alot of patience. It sounds like Mo is coming around!

Good luck! Sounds like Mo has a wonderful furrrever home!!