In 2006, film student Alex Kralie began work on his first feature-length film. Titled Marble Hornets, it was about a guy returning to his childhood home after a lengthy absence. Kralie and his friends were rather excited about working on it. After two months of on-and-off shooting, Kralie suddenly canceled the project, claiming it to be due to "unworkable conditions." Jay, his friend, asked him what he was going to do with the tapes. Kralie replied flatly:"Burn them."After much arm-twisting, Jay persuaded Kralie to at least give him the tapes, to which Kralie agreed under the condition that they were never mentioned to him again. Kralie transferred to an out-of-state school, never speaking to Jay or anyone else again. Jay, spooked by Kralie's comments, filed the tapes away and forgot about them. Until July 2009. - tvtropes.com
and small blurb from Roger Ebert
“Marble Hornets,” a YouTube serial. A forsaken indie film meets “Paranormal.”
This is probably one of the best series based on the slender man currently being produced.
Here are some other good series relating to the slender man