i need help to lock but still locate my iPhone xr it has all my information plus some and i believe its off but does not show up on the find my iPhone page

find my iPhone is not working on my computer to locate and lock my device it could be off or hacked I'm not sure. my apple id still shows it as one of my devices but not on the Find My iPhone page my previous other devices do though and that bothers me as my business account info, bank, and important legal documents are on my stolen device please could some one help me