How to track down a Night Creature in a city?

Solution 1:

If you offer service to the people of the city where the creature hides, and the quest they're offering you is to hunt down that particular creature, they'll guide you (for example, saying that the creature hides in a leatherworking shop to the South).

A good place to look is in the official buildings - vampires often ascend to important ranks. Vampires with lots of kills might also wear a lot of jewellery made from their victims.

Other than that, there's no simple way.

Solution 2:

DFHack have command cursecheck to check for cursed creatures (ghosts, vampires, necromancers, werebeasts, zombies). You can check creature under cursor, it will save fome time from talking to every person.