Under the new tax law that was passed in 2017, there is no federal tax deduction for thefts for years 2018 through 2025. There is an exception for Ponzi schemes, but it doesn't sound like that is your situation.
It's possible that your state might allow a deduction on the state tax return.
(Technically you could claim a federal deduction if the theft is a result of a federally declared disaster, but realistically disasters do not cause thefts. And in any case, that doesn't seem to be your situation either.)
Form 4864 cannot be filed by itself. It has to be included in your tax return. But it doesn't matter, since you can't claim the theft loss anyway.
