Which is correct?

My whole family is worried because one of our cat seems to have disappeared.

My whole family is worried because one of our cats seems to have disappeared.

My whole family is worried because one of our cats seem to have disappeared.

None of these

The correct sentence is: "My whole family is worried because one of our cats seems to have disappeared."

"Cats" agrees with "one of" and "seems" matches the singular subject "one of our cats."