SOLVED. Sci-fi mystery A guy lives in a city where it's always day in one half and night in the other. [s]

[Manolya]

The guy is hired to find a missing teen girl by her parents. He lives on the day side but has to go to the dark side and city outskirts. There is this creepy foggy place between to two sides, so he has to take the train to get there. And the guy constantly worries about his watch.
prob from 2015-2017

[Mai]

Searching "novel" "sci fi" "night" "day" "city" "missing teenager" this book came up:
A Man of Shadows by Jeff Noon (published in 2017).
Below the neon skies of Dayzone – where the lights never go out, and night has been banished – lowly private eye John Nyquist takes on a teenage runaway case. His quest takes him from Dayzone into the permanent dark of Nocturna.
As the vicious, seemingly invisible serial killer known only as Quicksilver haunts the streets, Nyquist starts to suspect that the runaway girl holds within her the key to the city’s fate. In the end, there’s only one place left to search: the shadow-choked zone known as Dusk.

[Kris]

Shelving as I see this request is marked Solved and A Man of Shadows by Jeff Noon appears in the topic header.