Do you think this is like the original FNAF in the sense that a bunch of things are just, swept under the rug. Like "Oh no somebody went missing at our establishment! Anyway-"
No one’s going missing within the establishment! At least not to Martyn’s knowledge.
He did however catch wind of Shelby’s disappearance when her mother barged into the building and began frantically interrogating the closest employee within arms’ reach. Martyn had to firmly pry the lady from Cleo’s shoulder before having her escorted from the building.
Though the encounter could’ve been easily dismissed, he did do a quick check that night of the security footage for the main restaurant. Sure enough, no footage indicated Shelby had even clocked in that night.
So the girl ran away, is his running hypothesis.