Police believe missing local community activist and library campaigner Robbie Gibson may have travelled to Hampshire and the Isle of Wight.
They have renewed appeals for the public’s help to trace him.
He left his home in Gipsy Hill at 3pm on Monday 13 June to go for a walk.
He was last seen later that day in the Co-operative store on Central Hill in Crystal Palace.
Officers have since been informed that Robbie was seen at 6.45pm that day catching the catamaran from Portsmouth to Ryde on the Isle of Wight.
He is believed to have boarded a train at Ryde Pier Head station towards Lake and Shanklin.
Police have released a CCTV image in the hope that someone may know where he is staying.
Robbie is known to enjoy coastal walks and often stays on campsites.
His family and friends are growing increasingly concerned for his safety and wellbeing and have launched a fundraising campaign to help the search for him.
Robbie is described as white, 6ft tall, of slim build with grey/silver hair. He wears black-rimmed Prada glasses.
He is likely to be wearing a blue/grey teeshirt with green/brown khaki trousers.
Anyone with information on his whereabouts is asked to call police in Lambeth on 101 or the charity Missing People on 116000.