I agree the frist place to start is a vist to the vet. Our Little Bear was very thin ( 6 lb ) and feeding a kitten. Our vet recomended that we start her on kitten food, she is still feeding the kitten but she has also gained 1.5 lb over the last 3 weeks. Her coat is now shinny and soft. The kitten food is high vitamin and high fat. We will be feeding it untill the kitten is weened. I hope to get upto about 9-10 lb.
Again please check with your vet.