A 30-year-old man has been arrested in connection with the murder of Tanesha Melbourne who was gunned down in Tottenham on Monday.
The 17-year-old was killed in a drive-by attack as she sat chatting with friends.
The killing shocked the capital, which has seen a rising wave of violent crime with the number of suspected murders in March higher than that of New York.
The Met Police said on Friday that a man had been arrested in Hackney, east London, on suspicion of murder and is currently being held in custody.
Police were called to Chalgrove Road at 9:35pm on Monday following reports of gunshots.
Paramedics battled for an hour to save her life but she was pronounced dead at the scene.
Just 30 minutes later, 16-year-old Amaan Shakoor was shot in Walthamstow and died in hospital the following day.
Officers said they are keeping an open mind about the attack, and at this stage there has been no suggestion that the two killings are linked.
Detective Inspector Beverley Kofi, of the Homicide and Major Crime Command, said: "We are appealing to anybody who witnessed the incident and has not yet come forward, or who in the hours since this shocking murder are privy to information that could help us find those responsible.
"You may be fearful of repercussions of speaking to police, or have loyalties that you believe can't be compromised.
"We are dealing with the fatal shooting of a teenage girl, and would implore you to do the right thing and come forward."
It emerged on Thursday that the Met has opened 55 murder investigations in London this year and there were six non-fatal stabbings from Thursday night into Friday morning in the capital.