A 16-year-old boy was arrested in the Hackney Area on June 22 as part of the investigation.
Another 16-year-old boy was arrested on June 17, he has since been released on bail.
A 18-year-old man was also arrested on June 7 but later released on bail pending further enquiries.
In many of the incidents, lone women had been walking or jogging when they have been approached by a male on a bicycle.
The male then proceeded to grab them from behind or touch their genitals or breasts before making inappropriate comments and leaving.
Detectives are continuing to appeal for information regarding the linked-series of attacks and last week released an E-fit of a male they were working to identify.
Detective Superintendent Mike Hamer, from the Central East Basic Command Unit, said: “We have now made three arrests in connection with these sexual assaults and our investigation continues at pace.
“I understand these assaults have caused considerable concern among the community, but we have a dedicated team of officers working around the clock and carrying out a number of enquiries to bring the perpetrator to justice.
“This investigation is a priority for my team and we’re taking it extremely seriously.
“We also have an increased police presence in the area, and officers are speaking with members of the community to provide reassurance. Anyone with any concerns can speak to these officers or call 101.
“We are continuing to appeal for the public’s help and we would ask that anyone with information that might help our investigation, or any victims who have not yet come forward, to contact police as a matter of urgency.”
Anyone who has information that could help police should call 101 or Tweet @MetCC and quote CAD 2905/22JUN
To remain 100 per cent anonymous, contact the independent charity Crimestoppers on 0800 555 111 or online at crimestoppers-uk.org