Could my fish have been eaten?

In my 10 gallon fish tank, we have a pleco and a black skirt tetra. I just bought three more black skirts and five neon tetras. The old black skirt is about 2 inches long, and the new ones are about 1 inch. The pleco is roughly 5 inches long. The neon tetras are all shorter than an inch, and one of them is missing. The four remaining are all huddled in a group in the back corner of the tank, where they've been for several hours now. What happened? I'm sure it hasn't jumped out of the tank, and it couldn't get sucked into the filter.