I'm an author of sf and crime fiction.  I have a Facebook page to announce new books and stories and other such news, and I regularly get friend requests from people who read me.  But over the past year or so I've been getting requests from young women (and occasionally young gay men).  When I check the requester's page I usually find nothing but a couple of posed pictures.

Back when all this started, I clicked "confirm" on a couple of requests.  The next thing I knew, I was getting ads for shoes and fashions on my wall.  I defriended the shills and the ads stopped.

So mostly it's just seems to be people trying to make money through clicks on Facebook ads.