looks soooo skinny, put him in another cycled tank and make sure you start to fatten him up. but don't over feed... he'll fatten up and at least not worry about that. make sure that there is a lot of hiding places for him and if he is still interested in food might become healthy again.
NTD disease: Infected aquarium fish will often spend less time with their schoolmates than normal, typically hiding away under aquarium plants and showing no interest in fish food. The aquarium fish’s colors fade, and sometimes gray or white patches on the flanks become apparent. In advanced cases the aquarium fish may have trouble swimming, and the fish may develop odd swellings or contortions indicative of damage to the musculature. Usually the aquarium fish dies within two or three days of the first symptoms of neon tetra disease becoming apparent.
Unfortunately for the aquarist several other diseases can cause similar symptoms to neon tetra disease, including systemic bacterial infections, chronically poor diet and/or environmental conditions, and even old age. Some aquarists have coined the term “false neon tetra disease” to refer to bacterial infections with broadly similar symptoms.