Police were called to Dog Lane, NW10 at 7.01pm on Monday, 15 August following reports that a person had been shot.
Officers attended and found a 17-year-old male with a gunshot wound.
Two further victims – a 21-year-old man and another man believed to be aged in his early 20s – were found nearby.
All three males were transported to hospital.
The 17-year-old’s injuries have been assessed as non-life changing, the 21-year-old has a potentially life changing injury and the man believed to be in his early 20s remains in a serious but stable condition.
Police firearms officers responded as part of the incident.
They provided emergency first aid to the victims until the arrival of paramedics.
An investigation is under way. At this early stage there have not been any arrests.
Anyone with information should call police on 101 with the reference 6551/15AUG.
Information can also be provided to Crimestoppers, anonymously, on 0800 555 111.