Animals can be dangerous when they're hurt and in pain or lost and scared. If you're concerned about approaching them, call the ASPCA right away.
If you feel the injured animal is safe and small enough to handle, take them to your nearest veterinarians' office to be evaluated and treated if necessary. The animal might be microchipped, and a veterinarian will be able to check for this. All vets will administer emergency care to an animal in need.
If you can safely manage it, check for a tag or other identification. There might be a license number, address, or phone number for the person who owns the animal or for the location that it escaped from.
If the animal is loose but not injured and without tags, contact your local ASPCA or the nearest no-kill animal shelter.
If the animal is on the roadway, contact the police immediately.