Boo (2005) on Netflix

Plot summary

Kevin and two friends, Freddy and Marie, ask Jessie Holden to join them for one Halloween night inside Santa Mira Hospital, which closed years ago after a fire. Another friend, Emmett, is already there arranging props meant to scare Jessie. Allan, meanwhile, is hunting for his sister Meg, who went missing in the same building days before with her friend Caitlin. He asks Arlo Ray Baines, an old friend of his father, to come with him; the former actor, now a cop, turns him down and then trails him anyway. The two groups run into each other on the third floor, in the wing that once held mental patients.