A 16-year-old boy was wounded in the leg during an attack in Manor Road, Chigwell, shortly before 8.55pm on Saturday, July 5.
Essex Police believe a large group may have been involved.
A separate incident took place the same evening at Chigwell tube station, where another 16-year-old boy was robbed by three masked men who stole his phone and money.
Chief Inspector Terry Fisher, district commander for Epping Forest, said: “I know these incidents will cause concern among our community but I have a team of detectives working to identify those involved and to establish if there is a link between the two incidents.
“I have ensured there are additional high visibility patrols in the area to provide reassurance so if you have any concerns or information please speak to them.”
Officers are appealing for witnesses and are urging anyone with information, CCTV, dashcam, or other footage to come forward.
Reports can be made through the Essex Police website or via the online live chat service, which operates 24/7.
Anyone wishing to remain anonymous can contact Crimestoppers at crimestoppers-uk.org or by calling 0800 555 111.
The crime reference number is 42/94408/25.
