A 34-year-old man from Lambeth has been arrested in relation to eight sexual assaults in the Clapham area that detectives believe are linked, the Metropolitan Police said.
The attacks have targeted lone women late at night in residential areas and all victims were aged in their 20s and 30s.
Another man was arrested and then released on bail on Wednesday but police were still looking for other people.
Superintendent Rob Applegarth of Lambeth borough, said police had increased patrols in Clapham and Brixton Hill and women were urged to consider their personal safety.
He said: "We are aware of eight assaults which we are linking at this early stage."
Five of the incidents have occurred this week but the string of offences began in Clapham on Friday October 9.
A 23-year-old woman was grabbed on Clitheroe Road and assaulted, but the suspect ran off when she raised the alarm.
Early the following morning, a man tried to engage a 30-year-old in conversation before grabbing her on Deauville Court.
Incidents became more frequent
Last Thursday, a 32-year-old victim was followed along Trent Road by a man who put his hand up her dress.
The incidents became more frequent this week, with three attacks on Monday evening - involving women aged 35, 28 and 26 - in as many hours.
The youngest of those victims was recorded on CCTV being approach from behind by a suspect as she tried to enter her home.
In a statement, the Metropolitan Police said: "The CCTV has been released by officers along with a still image in an effort to identify the man as soon as possible."
The most recent attacks, which both happened on Wednesday evening, involved a 28-year-old and a 31-year-old.
Detective Sergeant Gordon Barclay, who is leading the investigation, said: "We have had a good response following previous appeals."
He added: "We would still like to advise women to remain vigilant when travelling at night and would also ask that anybody who may have any information regarding these offences to make contact with police."
Anyone who has any information or witnesses should to call the MPS on the police non-emergency line on 101.