I know who these guys are. They do have accounts here, but that's not really the point.
The bottom line is that they're trolling you. If you don't send them messages, they won't bother you anymore.
I've said this before, but open disclosure: it's pretty easy to tell how old most of you are based on what you post. Youth makes you targetable as a joke. You'll understand why in due time.
To be clear, they're not malicious -- just need to find something better to do in all honesty. If it makes you uncomfortable, then tell me and I'll ask them to stop. They will.
They'll probably have a crack at me for this post, and because I'm the mod who has to spoil things. But whatever. I'll cop it. :]