Lambeth Police are appealing for any information or witnesses to two incidents on the South Bank in the early hours of Tuesday 11 August.
In the first incident a man and woman, both aged 31, were walking along the riverside towards Oxo Tower Wharf at about 2.20am when they were approached by a group of 10 people – eight men and two girls, all believed to be aged in their early to mid teens.
Some of them began to talk to the two and then suddenly a member of the group began to attack them with bottles. The woman's bag was taken.
Both victims were taken to hospital suffering from cuts and facial bruising. They were later released.
Jonathan Morrison, who was with his girlfriend Kathryn Donovan, told The London Paper this week: "We were by the Royal Festival Hall when we saw the gang drinking by the river. They looked quite respectable – clean cut. I remember one was white, tall and skinny with blonde hair.
"They suddenly attacked us. One came at me with a bottle and someone hit me round the head with another bottle. I don't remember much else because I was knocked unconscious."
One of them, a 24-year-old man, was headbutted when he refused to hand over any money. The group then moved on.
The incidents are being investigated by Lambeth CID. A number of people have told police they saw this group and had been approached but not assaulted.
Descriptions of the suspects include a white boy with a long face, around 6ft tall and slim; a white girl wearing a leather jacket, shorts and knee high boots and a young black man with a black and yellow New Era cap and matching t-shirt.
DI Jon Freeman of Lambeth CID said: "Attacks such as this are not common and I would appeal to anyone who was in the area – did you see anything of this large group of people? Does any of this description sound familiar?"
Officers are examining CCTV footage from the area.
Anyone with any information should contact Lambeth Police on 020 8649 2840 or Crimestoppers on 0800 555 111 if you wish to remain anonymous.