I would definitely be calling the vet...Acetaminophen (tylenol) is toxic to dogs, and 500 mg sounds like quite a bit for a small yorkie...
Acetaminophen Toxicity in Dogs "There is no home care for acetaminophen toxicity. If you suspect that your dog has ingested a toxic amount of acetaminophen, (one pill or more), contact your family veterinarian or local veterinary emergency facility immediately."