The meaning that you want to convey isn’t clear. You need to better explain the scenario. Natural to say are things like: Who did I forget? Who did I forget to count? Have I missed anyone?

"Who's missed?" means that you're asking someone to see who's losing the chance to be there at that time. "Who's missing?" means that you're asking around to see who's not available or lost. So the second question is correct!

Whom have I missed? Who is missing?