One my cats, Bass, was incredibly shy at first. She hid for the first couple of months, only coming out to eat and use her litter tray when she felt it was safe.
Could you bear to have his litter tray and food bowls in the bedroom for a few days?
A Felliway difuser really helped Bass - it won't work miracles, but it's worth a try. It takes a few days to start working and you need to put it in the room he's in most of the time.
Has your new boy got a box or something he can hide in - somewhere he can retreat to and call his own? A cardboard box turned upside down with a hole in the side, perhaps?
Talk to him, even if it's just rubbish! He'll eventually come and see you, just out of curiosity. I used to talk to Bass in a silly voice, because I was worried I sounded tense and anxious and didn't want to make her worse!
Other than that, it just takes time, especially if he's naturally a nervous cat.
Good luck!