This is a frustrating trophy to obtain because it relies on random chance, and no in-game clues are offered as to their location.
Anyways, the five locations are as follows:
Ijinchu:
- Honk-Honk Girl: An alleyway south of Survive Bar.
- Honk-Honk Lady: The small underground section immediately north of Wette Kitchen
- Honk-Honk Man: In the courtyard behind Sunlight Palace, in furthest corner. Chapter 11 or later.
Sotenbori:
- Honk-Honk Woman: In the south end of the secluded courtyard, east of the taxi stand at the bottom of the map.
Kamurocho:
- Honk-Honk Princess: In a small alley behind one of the buildings on the south side of the Hotel District main street.
You will likely need to try these locations many times. The common belief is that these characters will appear only after taxing a taxi, so you might be going back and forth a bunch. For me personally, it took 20+ attempts before each of Honk-Honk Man and Honk-Honk Princess appeared, but the other three were all there the first time I checked.