Officers found the teenager lying in a lane near Ladyford Avenue in Kilwinning at about 2.30am on Saturday, 22 May following reports of a disturbance at a property nearby.
Emergency services attended and the man was taken to Crosshouse hospital where medical staff have described his condition as critical.
Police have confirmed the disturbance involved a group of male and female youths, aged between 16 and 20, who were seen in Ladyford Avenue and the adjacent lane where the injured man was found.
Officers reported “a lot of shouting” had been heard in the area and that the group ran off before they arrived at the scene.
Detectives are treating the incident as an attempted murder and are reviewing CCTV footage and appealing to the public for any additional information.
Detective Chief Inspector Mick Carr said: “A group of youths were involved in a disturbance in a lane at the rear of properties in Ladyford Avenue, so I’m sure people will have heard or seen the disturbance. I would appeal to local residents who have any information about this incident to contact us. Any small piece of information could prove vital so please do pass it on. We are conducting extra patrols in the vicinity and want to reassure the public that extensive enquiries are ongoing by dedicated officers.”
Anyone with information is asked to call Police Scotland via 101, quoting incident number 0504 of 22 May, 2021.