Angel Whispers (2015)

Sham Shui Po is the most famous red-light district in Hong Kong. Li (Carrie Ng) owns a few of the apartments in the building and earns a living by renting them out to the prostitutes, to whom she is more a friend than a landlady. She gathers a group of them to work as hard as they can, trying to attract business to turn the tide; still, they don't know that they're quietly approaching death. It begins when prostitute Ping, who lives in the building with her young daughter, goes missing. As she searches for Ping, Li discovers that many prostitutes from the building had gone missing and none were ever found. The building was somehow isolated from the outside world and a massacre begins. Li and the prostitutes must find Ping and fight a battle of wits with the invisible murderer. As more evidence of the murderer's identity is revealed, a tragic truth hidden for over 20 years emerges.