Ponzi scheme losses are accounted for in a different section of Form 4684 than losses involving property:
SECTION C—Theft Loss Deduction for Ponzi-Type Investment Scheme Using the Procedures in Revenue Procedure 2009-20 (Complete this section in lieu of Appendix A in Revenue Procedure 2009-20. See instructions.)
The entries in that section refer to investments rather than property.
See this thread for another discussion of Ponzi-type losses.
The scheme is defined in the following federal links. It's important to review for your specific situation, the year of the known loss, recovery year or years.
You will use Form 4684, Section C to claim your loss if applicable. Note that recovery in a future year will be income after taking the loss.
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