The film stars Joey King, Julia Goldani Telles, Taylor Richardson, Jaz Sinclair, Annalise Basso, and Alex Fitzalan with Javier Botet as the title character.

In the fictional small town of Winsford, Massachusetts, Hallie Knudsen, Katie Jensen and their friends Chloe and Wren approach a group of boys to probe their evening plans, but they are told that it is top secret.

Deciding to hunt for clues at her dwelling, the other three recover her laptop, discovering that Katie, who had been unhappily living alone with her alcoholic father, had become involved in the occult, developing an unhealthy obsession with Slender Man sightings and videos and messaging Allison Riley, also identifiable by her online handle "AlleyKat93", regarding methods of reaching the character, who would spirit her away from her currently miserable environment.

Allison explains that he infects people’s minds similar to a virus, eventually either driving them completely insane or kidnapping them, and to retrieve Katie from his clutches, the trio need to "unveil themselves", which they interpret as surrendering an item that is very special to each of them.

Wren brings a piece of handmade pottery that she created when she was five years old, Chloe offers a picture of her and her father taken prior to his passing a few months afterwards, and Hallie relinquishes her younger sister Lizzie’s blanket, woven by their grandmother upon her birth.

Having researched Slender Man mythology, Wren instructs Hallie and Chloe to don blindfolds and warns the pair against removing them or opening their eyes to look directly at his face while contacting him, even if they hear something, for fear of death or madness.

After Hallie dissuades her from committing suicide, Wren, feeling guilty for causing the recent chain of events, breaks down and confesses that Lizzie approached her with interest in the Slender Man and asked that she accompany her to the woods, where she offered her teddy bear to him.

In May 2016, news outlets reported that Sony Pictures had started developing Slender Man, a film based on the supernatural mythical character created by Eric Knudsen,[4] with the screenplay to be written by David Birke.

[5] In January 2017, Sylvain White was announced as the director of the film and the producers would be Mythology's James Vanderbilt, and William Sherak, Madhouse's Robyn Meisinger, and No Dream's Sarah Snow.

The website's critical consensus reads, "Slender Man might be thin, but he's positively robust compared to the flimsy assortment of scares generated by the would-be chiller that bears his name.

[2] David Ehrlich of IndieWire gave the film a D, writing "a tasteless and inedibly undercooked serving of the Internet's stalest creepypasta, Slender Man aspires to be for the YouTube era what The Ring was to the last gasps of the VHS generation.