He creeped the silly goose out of me, until I came up with a theory. It is said that Slender Man will more likely come after you if you fear him, and leave you alone if you don't. He lives only to scare you. Sounds familiar to something, doesn't it? I call it fear. Slender Man IS fear. Fear will always chase you. Fear only comes after you if you fear it. It all seemed to fit in place for me, but it doesn't explain the sightings.
Edit: I can't have proof. I'm not saying he's real, I'm saying he could exist. I'll be back in like 10 mins. I'm going to search google for those pictures drawn by little kids and some quotes. BRB.