How to find villagers on the map
NPCs move around; the map preview tracks residents in your current area.
Finding someone
The August diary says NPC markers appear when you share the same area. Changing areas updates which residents the map displays. It does not describe a worldwide locator.
Why a villager has moved
Villagers are designed to follow routines, visit different places and interact with surroundings. Looking only where you last spoke to someone may miss them.
Development status
The launch announcement confirms a new map. The marker behaviour comes from a work-in-progress diary; exact schedules are not verified.