Adam Mitchell is believed to have been in a pub in Inverness' Baron Taylor Street on Wednesday night last week.
Police Scotland said CCTV images show him near the Harry Fairbairn BMW garage on Longman Road at 00:52 on Thursday.
Coastguard and police helicopters and the RNLI's Kessock lifeboat were involved in making searches of Inverness Harbour and Beauly Firth.
The effort followed up on searches made earlier last week.
Family and friends said Mr Mitchell's failure to return to his home in the Culduthel area was out of character.
Mr Mitchell is described as 5ft 11in in height, stocky build with long mousy brown hair and a beard.
When last seen he was wearing a black leather jacket, a denim vest, black jeans and boots.
Air, sea and land searches were made over the weekend for a missing 18-year-old Inverness man.