I am going to sound like the most heartless person in the world, but there is a very good reason that most of us leave unhealthy chicks in the bin. It's wonderful that people feel the need to "do something" for a chick like that, but the bald truth is most of the time they die anyway. They most likely wouldn't survive if a hen was brooding them, either. By the time you're done trying this, giving that a shot, and doing the other thing, the chick's ultimate fate is probably not going to change. The only thing that will change is that he will suffer a little longer, and you'll be exhausted and beating yourself up for not saving him.
I know that is cold. Two years ago I was the person who would have chosen the poor little runt and tried to be the one to give it a good life. I know better now, and I know it's better to give my attention and affection to chicks that will grow strong and healthy, rather than prolong the suffering of a chick that, if it survives, will most likely need extra special help just to live a halfway normal life.
That said, I did spend months taking care of little chick who froze his feet on a cold, -17 degree day. There wasn't much I didn't do for him, and he not only survived but he thrived, only to have to be culled when he was 8 months old due to aggression issues. Lots of folks on BYC followed Scout's adventure and were rooting for him as hard as I was. Now I know that if I had it to do over again I think I'd skip the heroics. So the ultimate choice is up to you.
I'd start with getting some Nutri Drench into him...it's a nutritional powder that you mix with water. It's beneficial because it sends nutrition directly into the blood stream, rather than it having to be digested first. If you don't have any of that, you can try some sugar water. Keep him very warm, quiet, and when he's up to taking chick food I'd moisten it and hand feed it to him. Make sure he drinks. That's about all you can do. Good luck with him, and I apologize if I came across as hard hearted.