If the bird is fully feathered, it is most likely a fledgling and has left the nest on it's own and it's parents are caring for it. You need to replace it where you found it..preferably in a scrub or tree so it is relatively safe from predators, and the parents should come back to feed it. You should watch for at LEAST an hour to see if adults are feeding them. If truly abandoned...get them to a wildlife rehab. If it is unfeathered...then look for a nest and if you can find it...replace it into the nest. Do not worry about your scent being on the chick..birds have a very poorly developed sense of smell and will NOT reject a baby that has been touched. If you cannot find a nest, get the bird to a local wildlife rehab for it's best chance of survival. Also, keep in mind, it is illegal for you to try and raise this bird on your own. Look for a rehab near you here:
http://www.tc.umn.edu/~devo0028/contactA.htm