I’m so sorry about your Platy! Unfortunately, fish disappearing randomly happens a lot in the hobby; my only advice would be checking the floor around your tank like Aiken Drum said.
I have a few questions that can help you find her; did you leave your fish tank to someone else at least for a day?
Do you have any family members that could have taken your fish or went into your room filled with tanks? (I’m not implying they stole her, just asking if any young cousins or kids could have went into the room and “played” with your platy)
Did you check the aquarium ground throughoutly? She could have been buried very deeply into the substrate.
And the last one, do you have any pets that could have done the deed?
If you aren’t able to find her, let us know
Hope it helps!