I've been very confused by the two contradictory answers for this question. On further Googling I find there are very specific boundaries to when you can claim timeshares as a second home to claim the loss. You can't just "claim as a second home," unless you meet this criteria. You must live in in it for a certain amount of time of the year or rent it out or somehow use it as a business. If you had a timeshare and used it once a year for a week to vacation you can't claim the loss. Just another reason to be sad about owning the timeshare to begin with.
Here's a link to what the IRS has to say if you want to take a deep dive or need a distraction from working on your taxes:
https://www.irs.gov/pub/irs-pdf/p936.pdf
