If the business closed back in 2011, then I assume you received a final K-1 in that year as well?
Assuming the first statement is correct, you should have also been maintaining a basis schedule for your investment in this entity. You would have then determined your overall gain or loss on this investment and reported it on your 2011 tax return.
At this point if you were a guarantor of the note and had to make good on it, then this is handled the same as if you had made a capital contribution. However, at this point there is no business and this "capital contribution" is treated as a capital loss on your Schedule D and applicable for 8949.
Having said that, you need to be careful in the amount of loss you claim. If there are other individuals that guaranteed the debt and you have the ability to seek reimbursement from them, then you may not have a loss for the total amount that you paid the bank (only your portion). You would need to make an attempt to seek reimbursement. Once you have gone through that process and it is determined that you will not be reimbursed, then you would be able to claim a loss for that portion of the guarantee you paid.
If when you guaranteed the note you waived your rights of subrogation (meaning you will not attempt to collect from any other member / shareholder) then you would get to claim a loss for the full amount.
*A reminder that posts in a forum such as this do not constitute tax advice.
Also keep in mind the date of replies, as tax law changes.
