This is probably a non-business bad debt and is reported in the same way as an investment loss. You can deduct the loss against other investment gains, if you don't have investment gains, you can deduct up to $3000 per year and carry the rest forward until you use it up.
https://www.irs.gov/taxtopics/tc453
https://turbotax.intuit.com/tax-tips/irs-tax-return/how-to-report-non-business-bad-debt-on-a-tax-ret...
Somewhat strangely, this is reported in the "Income" sections under "Sales of stocks, bonds and other assets." I believe you list the asset type as "Other", and then you will get some questions about the type of loss and you should be able to select bad debt as one of the options. The purchase price is what you paid and the selling price is zero (assuming the debt is worthless).
Note you can't claim a bad debt deduction until your loss is final. That means that if the bankruptcy proceeding is ongoing and there is a chance you will be paid something (even if only a little of what you are owed) you can't claim the bad debt deduction. You have to wait until the proceedings are final and there is no chance of recovering any more of your loss. (For example, if the bankruptcy is in court until 2023 and you eventually get repaid $500, you could take the deduction on your 2023 tax return in the amount of $13,500, but you can't take it now because it is not final.)
You also have to make bona fide efforts to collect. If the travel agency has a legal bankruptcy case, you must get yourself listed as a creditor on the case. If they didn't file for formal bankruptcy, you must sue them in court, or take other bona fide and legitimate steps to collect. You can't just shrug your shoulders, walk away, and put it on your taxes.
Also beware, if this is categorized as a theft by the authorities (for example, the police arrest the travel agents and charge them with stealing funds from their clients), that converts this from a non-business bad debt to a theft loss, and theft losses are not deductible after 2018 tax reform. Hopefully that will not come up in this case. To be a bad debt and not a theft loss, there has to have been a genuine and enforceable contract where you provided funds and the other party was supposed to provide something of equal value.
See also page 54 here https://www.irs.gov/pub/irs-pdf/p550.pdf
