Why did my Neon Tetra go missing?

Yesterday my tank was in great condition, or so I think. I have two Painted skirt tetras and one neon tetra. They were all swimming in unison and I never had problems before but when I came home today to check my tank the neon tetra was gone. Where could it have gone? the two painted tetra usually bully each other alot about territory but would they eat that neon tetra? it didnt seem to be sick or under stress. I'm baffled. Please help!