Pokémon in Pokémon Go tend to show up in various locations all over the game, depending on the area in the real-world. For example, if you visit a beach and power up the game, you can expect to see plenty of Ground and Water-type Pokémon wandering around, such as Krabby, Squirtle, Staryu, Horsea, and more.
For Ghost-type Pokémon, you need to be consistently on the lookout for them. Unfortunately, you have a lesser likelihood of encountering them during the day. You want to wait until nightfall drops in your area, and you can expect to see them spawning around you after 8:00pm, and they should continue to show up through the bleak hours of the morning until 8:00am, in your timezone.
It helps to visit different locations, too. Wandering around the streets before it becomes too dark is a good idea, but you don’t want to stray too far for it to become dangerous for you.
Another great time of day to wait for is when the fog rolls into your region. If it’s a foggy day, take out your smartphone and fire up Pokémon Go to see if any Ghost-types have spawned nearby. Many of them tend to show up during this type of weather, and it’s only for a brief time.
For those desperate to find Ghost-type Pokémon and don’t have time to wait for dark to arrive, you can always try your hand at waiting for raids. Various leveled raids may contain Ghost-type Pokémon, but these are random. It all depends on the month, and what the current rotation of Pokémon are available to spawn at these battles.
Make sure you keep your eyes on any available raids or those about to pop. You might find yourself with luck on your side, and a Ghost-type is possible to fight. Unfortunately, you need to rely on having a raid pass available, and if it’s a powerful Pokémon, it helps to have some friends willing to assist you.