My dogs have been on glucosamine for years. This is the dosing chart that I use. For such a small dog you might want to stay away from the human pills. They will need to be cut up and it can make dosing a pain.
Glucosamine:
Dogs 5-20 pounds: 250-500 mg
Dogs 20-45 pounds: 500 mg
Dogs 45-90 pounds: 1,000 mg
Dogs more than 90 pounds: 1,500 mg
Chondroitin:
Dogs less than 80 pounds: 900 mg
Dogs more than 80 pounds: 1,800 mg