Generally, there are two kinds of bad debts. Business and non-business. Here is a link to Topic No. 453, Bad Debt Deduction on the IRS website. I suggest looking at that topic and the related links. Your question lacks some specifics to make a determination as to whether this would be a business or non-business bad debt. My first impression is that you are/were an LLC member that loaned the LLC money. Depending on further relationship, duties, etc.,etc., I would also have an initial impression this would be a nonbusiness bad debt, which would be deductible as a short term capital loss.
But, please review the topic and related links for further and more detailed information that will fit your circumstances.