A gang in a 4x4 car threatened a teenager with a baseball bat then chased him along the road as he tried to escape on his moped.
The incident happened between 8.30pm and 9.30pm on Tuesday, February 5, when the 17-year-old was riding his moped along London Road, Ewell, near to the junction with Kingston Road.
Four men threatened him by stepping in front of his bike and trying to strike him with a baseball bat.
They then pursued the youngster through roads in the area in a green 4x4, at one point reversing the wrong way down the A240.
The youth was not injured in the incident and no arrests have been made.
Detective Constable Antony Preston, of Epsom CID, said: "This was a terrifying ordeal for the young man involved and we need anyone who witnessed any part of this incident to contact detectives with information.
"At this stage in the investigation we do not believe that these were random threats and that the victim and the offenders are known to each other."
Anyone with information should call the police on 101 quoting reference EP/13/604 or Crimestoppers on 0800 555 111.