The police helicopter was also called in during the search
Armed police were in Borehamwood on Saturday after reports of a moped rider holding knife.
Officers rushed to the scene in the Aycliffe Road area of the town shortly after 5.30pm on Saturday and were joined by a police helicopter to search for the moped.
Hertfordshire Constabulary says it received a report of a "moped chasing a vehicle along Aycliffe Road" and the moped rider "appeared to be holding a knife".
In response, a number of units were sent to the area but following a search neither the moped or vehicle reportedly being chased were traced.
Enquiries are continuing.
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