If you have access to an avian vet you should take the chick for an exam. If you can't get the chick to a vet, the next best option would be a reputable breeder that has experience hand feeding chicks, they could recommend a formula and tell you how much and how often the chick should be fed.
You should keep the little guy warm and clean and give him something more comfortable than thin wire mesh to stand on.
You should never give antibiotics that were not prescribed by a licensed vet, the wrong antibiotic or the wrong dosage can result in your bird's death.
I hope your little chick recovers, please let us know.