They’ll try to start some kind of online relationship, then when you are on the hook tell you their mother or niece needs money for an operation.
My guess is that it’s rarely actually a ‘hot girl,’ but – far more often than not – a scammer (invariably male) who figured he has a better shot at getting in with you if he poses as a hot girl.
That’s very likely, and even if the person is a woman it’s not an actual photo of them.
I am active in several Facebook groups (Stray Shopping Carts of North America, Park Bench Appreciation Society, International Scaffolding Enthusiasts, etc) and so often get Friend requests from fellow aficionados. If we have no mutual Friends or interests the request is deleted.
On the other hand, I just now saw two attractive young women in my “People You May Know” list. I have no idea who they are, and unlike most suggestions they don’t show any mutual friends to me. I wonder how they get on that list. My best guess is that for some reason they checked my profile (maybe in order to send a scam friend request).
Looks like this guy has some evidence that “People You May Know” with no mutual friends may be ones who looked you up.
I guess I take a bit of a different tack here. If I see a friend request, I’ll look at the person’s info and if there is something worthwhile like cool photos, or if they just seem like nice people, I’ll accept the request. I’ve gotten to know a couple dozen people from different parts of the world, in a superficial but enjoyable way. Nothing bad has ever happened to me from doing this.
I accepted a friend request from my late mother a few days ago, because I was bored and felt like playing games with a random scammer.
I’m frustrated that there doesn’t seem to be a way to report the cloned page to Facebook. I can report but not with explanation and they just keep telling me the fake page doesn’t violate their community standards.
From the faked profile, click the three dots on the far right. One of the choices is “Find support or report profile.” Click it. Choices include “Pretending to be someone,” “Fake name,” and “Fake account.”
When I’ve gotten friend requests from the spoofed account of a friend or relative, I’ve reported them and sometimes it’s gone within minutes.
The ability to report a fake account is not always obvious - but I do when I can find it. I also let the real person know that they’re being spoofed.
I periodically get friend requests from men who are total strangers to me. Usually 50ish and widowed. 
Usually they have no friends yet. There used to be a way to report them as likely scammers but I can’t ever find that link any more.
In both cases, delete, delete, delete.
Like BobLibDem , I use the rule of “If it’s a hot girl, it’s spam.” I don’t prowl Facebook for hot girls, anyway. However, I have a shred or two of pity for actual, genuine hot girls who can’t find any Facey friends, because so many of us reject them out of hand. 
I just got a friend request from an attractive young woman I had never heard of. However, most such requests come from women who look very glamourous, often with exotic names. She was pretty but otherwise ordinary looking. She was supposedly from New York, as I am. But she had not friends in common, and in fact show any friends at all. Of course, I deleted the request. I was just surprised because this one was so atypical.
Lots of my facebook friends are hot girls. They are all people I know, however, so it was easy to friend them on Facebook.
I get those too, and for some reason they are all extremely attractive older men. And they always have a dog, too!
I wound up setting my permissions so that I could only receive requests from friends-of-friends. Which stymied me recently when a former colleague and I were trying to friend each other - I think he had the same thing. I briefly turned it off, then back on.
I’ve been getting requests of late from friends-of-friends, but I ignore them. It would be different if my friend said "You should connect with < insert name here > because you both like < insert common interest > but frankly, a friend of my friend isn’t necessarily my friend. I don’t need to be connected with a gazillion people to feel validated.
“Keep your Facebook friends close, and the people pretending to be your Facebook friends closer.”
For a while, I was getting a lot of friend requests from people who claimed to be recently widowed men in their 50s (my age). We had no mutual friends, and I did the right thing and deleted them.
I was just friended by another mushroom enthusiast… who is an Admin or mod in a lot of groups I am in.
I guess my week-end rambles in off-ID groups are acceptable 
I also was friend requested by my hubby’s niece/nephew’s other side of the family.
I get excited when I get an FR from… peoplep peple… people who have a clue as to I am. I do delete the “anyone/everyone” spam friends.
Other than the 500+ back in the day farmville/mafia wars/FB games friends etc that are still friends but don’t like my kitty pics.
(They get weeded out kinda as birthdays roll around: no “likes” last year or… 7 years ago? Gone!)
I do have a lot of FB games friends and even FB news sites “friends” who do like or comment on my stuff.
I know: echo chamber.
But many have became friends in the sense I care about what happens in their lives. I enjoy reading about them and am sad when life doesn’t send cupcakes.
I wish FB let me read more about all of them like a decade ago did.
I liked one comment on a Friend’s wall and this guy friended me immediately. Then he messaged me. I thought for sure he was a scammer but the truth turned out to be weirder. He was a man camping in rural Australia. (“just me, my dog and my pet cockroach.”) Obviously I’m intrigued.
I asked if he was a writer because I friend a lot of writers and he says he writes nonfiction that’s so disturbing he’s lost friends over it. Turns out he’s made a big project out of interviewing and documenting serial killers and sexual predators. On top of that, he told me all about his life trauma within minutes.
I like the guy. I attract all kinds because I’m unruffled by most weirdness. It was a nice conversation. But definitely not what I was expecting.