The reports of suspicious clowns have led to schools being shut down, and police forces have warned people to be wary if they see anyone dressed as one.
New Haven, Connecticut banned clown costumes on Halloween after threats to schools.
Many sightings of scary clowns and reports of them frightening people have turned out to be pranks, and police have complained that is leading to a waste of their resources.
A spokesman for Connecticut police said: "This can cause major disruptions leading to schools, businesses and neighborhoods being placed into lockdown unnecessarily."
In Texas a 13-year-old boy was charged with making a terroristic threat after publishing a "clown's hit list" on the internet.
A 13-year-old girl in Virginia was charged after sending a message to someone posing as a creepy cown on social media, asking that they kill her teacher.
In Utah police said they had received scores of calls from the public asking what to do.
One man asked if he was allowed to shoot a clown if he saw one.
Jordan Jones, a professional who performs as Snuggles the Clown, said: "Everyone took this as a joke but it's really become serious now and I just want all these teenagers to know that it's not a game anymore. You're ruining my job and other actors around the world."
The bizarre phenomenon has spread to other countries.
In the UK police in Newcastle said they had received reports of pranksters dressed as clowns jumping out from behind bushes and chasing people down the street.
And in New Zealand, police were called after a clown was spotted at Porirua school.
