There was a recent tweet on the dev's Twitter that the wandering mode (presumably what will toggle the ghost) wasn't ready in time for launch and will come with a future update.
He appears in the pools in set locations. There is one at the bottom of the pool, he flickers in the middle of the room with the underwater walkway, he "chases" you during the locker section, and you can see him after you climb the statue in the mall bit if you go look back into the hallway before you leave.
I honestly wouldn't worry about it. Most of the sightings from the demo are gone, and the chase section doesn't do anything if he catches up to you now, he just stops.
