Yesterday, they released a fresh image of Mr Chalmers, wearing a light coloured jacket, which has a dark collar. It is believed he was wearing this jacket when he was last seen.
He is described as 5ft 5ins and of slim build, he is bald and wears glasses and a cap.
It is understood that Mr Chalmers travelled to Aberdeen beach before he went missing, and officers have been searching the Esplanade, Footdee and the harbour for him.
Yesterday, they were carrying out door-to-door inquiries around the area and have focused their search to the harbour.
Officers are appealing for anyone with information to call 101 referencing 3145 of January 2.
Police divers resume search of Aberdeen Harbour for missing 88-year-old Donald Chalmers