My Guppy isn't eating?

I have a 15gal tank with 12 fish. 6 Tetras, 3 Guppies, and 3 Platties. The tank is cultured and the PH is 7.0 and the temp is 80F. All of my fish are fine and dandy except for 2 of them. I know that 1 tetra cant become the leader so he is depressed but the smallest fish in my tank is a guppy and he wont eat. He rests all day only playing for a hours. Is he not eating because he is scared of all the other fish or does he have a disease and is going to die?