Sivaram is 27 and is missing from Kingston.
He was last seen at 13.18hrs on Saturday, 5 October in the Brompton Road area of Kensington, SW3.
Sivaram is Sri Lankan, and is described as being of large build, with dark eyes, dark rimmed glasses and black hair.
At the time he went missing, he was wearing grey trousers and a jersey, a black jacket and cap. He may have a calculator with him.
Sivaram, who has Autism and takes medication, is described as extremely vulnerable.
At the time of his disappearance he was on a day out in London.
He also has links to Surbiton.
Officers are increasingly concerned for his wellbeing and would urge anyone with information on his whereabouts to call police on 101 quoting CAD reference 3975/05OCT19 or Missing People on 116000.