I'd say take it to your vet. Otherwise, at that age, the best you can do is to try to insure that the kitten stays warm and gets a chance to nurse from mama.
We've had to actually "Hold mama down" while allowing a kitten to nurse in these circumstances. Sometimes you get a mother cat who just isn't a good mom...and sometimes a mother cat senses a disorder in the kitten's physical being and refuses to nurse it (a Darwinian choice).
I'll tell you now, though, that at that age, kittens tend to live or die, regardless of the efforts of humans (beyond feeding, that is).
Put a towel over a heating pad and put the kitten on it to keep it warm. Even if you can get the kitten to eat, if it is cold, it won't help the kitten. When the kitten's body temperature starts to drop, its system starts to shut down, and feeding it can actually harm more than it can help. You have to warm the kitten up to its normal body temperature and then you can try boiling some water and mixing one cup of sugar into one cup of boiling water, and after it cools down to the temperature where it is comfortable on your wrist (like with a baby bottle), give the kitten a few drops from an eyedropper. When they don't eat for a while, and especially if they have gotten cold, they get hypoglycemic. The sugar water helps to level out their body sugar again and then you can try getting them to eat. If the mother absolutely will not cooperate, you can give the kitten some cow's milk tonight until you can get to the store tomorrow to get some KMR (Kitten Milk Replacer). They sell it in most grocery and pet stores. It has instructions on the label for feeding, and there is a thread here from a week or so ago on how to raise an orphaned kitten. I hope the little guy is OK. They're so small and fragile at that stage of their lives.