Games like Alien Investigator
Games like Alien Investigator include Phasmophobia, Demonologist, Escape the Backrooms, Pacify, and Dead by Daylight. We matched them by the tags players give Alien Investigator on Steam (Horror, Action, Online Co-Op, Aliens, and Detective): closest matches first, and among equally close ones the better-known games.

Phasmophobia
Shared: Horror · Online Co-Op · Psychological Horror

Demonologist
Shared: Horror · Online Co-Op · Psychological Horror

Escape the Backrooms
Shared: Horror · Online Co-Op · Psychological Horror

Pacify
Shared: Horror · Online Co-Op · Psychological Horror

Dead by Daylight
Shared: Horror · Online Co-Op · Multiplayer

Lethal Company
Shared: Horror · Online Co-Op · Psychological Horror

Ghost Exorcism INC.
Shared: Horror · Investigation · Psychological Horror

Content Warning
Shared: Horror · Online Co-Op · Action

Left 4 Dead 2
Shared: Online Co-Op · Action · Horror

Backrooms: Escape Together
Shared: Horror · Online Co-Op · Psychological Horror

R.E.P.O.
Shared: Horror · Online Co-Op · Multiplayer

DEVOUR
Shared: Horror · Online Co-Op · Psychological Horror

Shift At Midnight
Shared: Horror · Online Co-Op · Multiplayer

In Silence
Shared: Horror · Online Co-Op · Psychological Horror

Alan Wake
Shared: Horror · Action · Psychological Horror

Species: Unknown
Shared: Horror · Online Co-Op · Aliens

Aliens vs. Predator™
Shared: Action · Aliens · Horror

Dead Space™ 3
Shared: Horror · Action · Online Co-Op

We Were Here
Shared: Horror · Online Co-Op · Multiplayer

Resident Evil 6
Shared: Action · Horror · Online Co-Op

Ghost Exile
Shared: Horror · Online Co-Op · Action

Nuclear Nightmare
Shared: Horror · Online Co-Op · Psychological Horror

Aliens: Fireteam Elite
Shared: Action · Aliens · Horror

Lunch Lady
Shared: Horror · Online Co-Op · Action