The following is the definition of creepypasta...
Warning:Do Not Add Creepypastas Onto Articles.
By definition, all creepypastas are fictitious and are internet hoaxes, however, they would not be considered cryptozoological or even a conventional hoax, as its stories, according to Creepypasta Wiki, were never intended to be believed by anyone. Since they are not factual or not intended to be believed at any time, they are not considered Cryptids or hoaxes.
Below is an exert from News.com stating the accuracy of Creepypasta.
"A TEENAGE girl’s brutal attack on her mother has been linked to an obsession with fictional horror figure Slenderman...It is believed the spooky figure was invented in a Photoshop contest on the Something Awful forums in 2009 and became the subject of online paranormal fan fiction. He is also the subject of a number of YouTube mockumentaries where he terrifies viewers by making an appearance at a person’s front door."