i just bought 2 kittens silver american short hair 4 months old..male n female..but the male one not really "friendly" yet but it already 1 month..what should i do..any comment?

try Petfinder.my
better check with a vet. Lack of appetite + losing weight could be signs of sickness.
if not, it could be fussy. Try using some different brand, or mix with strong-smelling canned cat food or some meat. or even fish/olive oil. some pet shops even carry the type specially for cats.
canned tuna/sardine (for humans) can be used but not everyday because cats can get sick if they eat too much