First things first
Welcome to YT
I am very sorry you are having problems with Tucker. Having him flown in at such a early age no doubt put a tremendous amount of stress on the little guy --
You might try grinding up some of the puppy kibble and add to that a tiny little bit of high quality canned puppy food mixed with some water. Then maybe you can "tease" him into eating a bit off your finger. Some boiled chicken brest put through a blender to make a yucky looking mush might also help enhance the flavor enough to get him to eat.
Good luck and please please keep us posted