A 12-year-old boy was attacked at the junction of Vauxhall Bridge Road and Udall Street, SW1 on Wednesday, 12 May.
At around 3.54pm, a man approached the young boy and grabbed him around the neck.
The man held the victim by the neck until a member of the public intervened at which point, he left, walking away in the direction of Vauxhall Bridge.
The victim did not sustain any lasting injuries, but was shocked by the incident.
Officers have released an image of a man they are keen to identify and are appealing for help from the public to identify him.
Anyone who has information that could assist the investigation is asked to call police on 101 or tweet @MetCC providing the reference 5207/12MAY.
Information can also be provided to Crimestoppers, anonymously, by calling 0800 555 111.