Well, a Proxie in the Slender Man Mythos is often applied as a term for a servant of Slender Man. It wasn't always this term that was used, but it is now begrudgingly accepted as the term for them, due to it's misuse and overuse making it commonplace.
Proxies, depending on the blog/vlog/format often come in different types. Vlog types tend to be stock standard Masky or Observer clichés, though there are a few interesting deviations out there. The most notable proxies are probably the blog types, such as cultists (what it says on the tin), hallowed/hollowed (brain washed or brain dead servants), and Agents (people who serve of their own free will). Then there are other, more specialist types such as Revenants.
But despite the fact that Proxies serve Slender Man, they are not all inherently evil. In fact some are very human, and display strong positive qualities. Examples include Don't Shoot The Messenger and Coyote is Awesome.