How old is he? When I have weak chicks I do a couple things to try and help them get a jump start...
A. Poly-Vi-Sol (WITHOUT added iron) couple drops on the corner of the beak and let them lick it up, couple times a day
B. Crumbled hard boiled egg mixed with plain yogurt and a little chick crumble. You don't want to force feed them, it can cause them to aspirate, but if you are patient and put a little bit on the corner of their beak and let them lick it up you can get some nutrition in them. It can take a little while, just a little bit at a time.
C. Apple Cider Vinegar (just a little bit) in the water, this is good for all chickens. It helps boost their immune system and helps them absorb vitamins.
Hope this helps, just try and get something nutritional in his system as quickly as possible. I've had this method work for me a couple times with listless chicks, unfortunately though, some chicks are just failure to thrive cases and can't be saved, but at least you know you did everything you can.