The 22-year-old barber, from Newtownabbey, County Antrim, has not been seen for almost a week.
He was last seen in the Carnmoney Road area of Newtownabbey shortly before 13:00 BST on Thursday, 13 July.
Officers have also revised details of what they believe he was wearing on the day of his disappearance.
Det Insp Chris Millar said: "It has now been established that Dean was wearing a short-sleeve maroon shirt, denim knee-length shorts and dark-coloured canvas shoes.
"He was wearing a gold watch on his right wrist."
Mr McIlwaine is 5'8" in height and of medium build.
He has dark hair, a beard and sleeve tattoos on both arms.
Anyone with information on his whereabouts is asked to contact police by calling 101, quoting reference number 121 of 14/7/17.
Police searching for Dean McIlwaine have released CCTV footage taken on the day he went missing as they renewed their appeal for information.