A 12-year-old girl was attacked by a man who tried to undo her jeans.
The incident occurred at Distillery Lane, between 3pm and 3.30pm on Sunday, November 25.
Detectives are investigating the attack and have appealed for information.
A wide police search of the area failed to find any trace of the suspect.
The man was said to be black, aged between 21 and 40, about 5ft to 5ft 2in tall.
He was believed to have used Lynx Darkness deodorant and was wearing a silver ring on his right hand.
Anyone with information should contact Colchester Serious Crime Team on 101 or call Crimestoppers on 0800 555111.