You’ve Been Summoned by Lindsey Lamar
You've Been Summoned's setup reminded me a lot of the board game, Clank! Legacy: Acquisitions Incorporated, mixed with Clue. It's designed to be interactive, casting you, the reader, as the newest employee at PI, Inc. Apparently they're a bit short-staffed, so you're assigned a case right from the top. You have all the files regarding the incident at Sophomore Manor at your disposal - to be read in the suggested order. You also have several historical items from the 1940s when Mary Sophomore and her twin sister also went missing. You do receive some helpful pointers from the boss along the way.
The case you've been asked to look at involves Sillian Parks. She was throwing a party with several friends and her twin sister, Jane, at the Sophomore Manor, when she went missing. She was eventually found, but comatose, and foul play was suspected. It's up to you, the reader, to put all the information and clues together to present...