A man is wanted for questioning over a series of "despicable" sexual assaults on buses, including on a 13-year-old girl, Scotland Yard said.
Six young women have made complaints over a man matching the same description on buses in Lewisham and Southwark, south-east London, but officers warned many more could exist.
The Metropolitan Police said a string of attacks took place on January 27, starting with a girl, 17, boarding a 176 bus at 3.15pm.
The suspect sat opposite her and struck up a conversation before intentionally falling onto her and groping her, the force said.
Then, at around 5pm, a girl, 13, reported being sexually assaulted on a 363 bus.
Later another girl of the same age reported a man matching the same description made her feel uncomfortable by engaging in a conversation.
At 5.50pm a 15-year-old boarded a 171 bus at Catford train station.
The suspect sat opposite her and touched her knee, the Met Police said.
Frightened, she got off the bus but the man pursued her and groped her before she managed to flee, officers added.
Scotland Yard said the first attacks were on two women, 22 and 17, on a number 12 bus in Dulwich at around 9.30pm on January 24.
The suspect is described as a black man in his 20s with short black hair and stubble.
He wore blue baggy jeans and a black bomber jacket with a white fur trim on the hood.
Detective Constable Alex Price said: "We are keen to trace the suspect carrying out these despicable attacks on young girls and women in public.
"Five victims have been targeted by this man and we believe there could be many more victims who are yet to come forward."