Facebook Marketplace will not lift a finger to help you, period. Don't even try. You can click 'report this ad' or 'report seller' but I can pretty much guarantee you literally nothing will happen.
Facebook has no functional customer service, and to be honest they've repeatedly demonstrated that they do not care that Marketplace is used to fence stolen goods. There is literally nobody behind the scenes at FB Marketplace who is going to care, or help you.
Point being: don't waste your time contacting Facebook.
Per: https://bikeindex.org/news/what-to-do-when-you-find-your-sto...
Scum of the earth, all of 'em.