First off sorry to hear about this I just went through the same thing earlier this year, it looks really skinny so I'm guessing it hasn't eaten for a long time.In my opinion you should take it to the vets ASAP as if it's something that can be treated it will have a better fighting chance. But one major killer is crypto which I lost my yearling Ember to, it's nearly non curable but reps have been known to live with it for long periods. I would try and keep it warm and comfortable and force feed by gently pressing down on its bottom lips and allowing it to clamp onto your finger. I went through this as I said earlier and I looked up every possible ailment she could've been suffering but the only person that you can rely on for an accurate diagnose of the situation is a vet. In the mean time I think you can get A and D dog food from the vet.