Mr Horn is non-verbal and walks with a shuffle.
He is thought to be wearing a light-coloured polo style shirt, a black and red coloured jacket, gym shoes and sweatpants or jeans.
Police issued an emergency alert in the Invercargill area last night but said "this has unfortunately not generated any information as to his whereabouts."
Invercargill residents are asked to search their properties, even if they have previously searched them, as Mr Horn is believed to be on foot and may have wandered onto a property.
Additionally, police have asked anyone with CCTV on their properties to review the footage and submit it to police if they see anyone who looks like Raymond.
Twelve Land Search and Rescue volunteers are out in the field searching today, and members of Amateur Radio Emergency Communications (AREC) group who are working with the incident management team.
