The attack, understood to have been carried out by a group of four or five teenagers, took place near Grove Lane in Handsworth around 7.30pm last night.
The teenage victim was stabbed in the thigh. He was taken to hospital and his condition has not been deemed as life-threatening or life-changing.
West Midlands Police is appealing for anyone with information to get in touch via the force's live chat at www.west-midlands.police.uk, open 8am till midnight, or call 101 anytime.
For those who wish to remain anonymous, call Crimestoppers on 0800 555 111.
Quote log number 4156 of 06/07/2020.