His family reported him missing two days later.
Since then, Canterbury police have interviewed his family, his two flat mates and witnesses who reported possible sightings of Mr Cossey in an effort to narrow down a potential search area.
Later this morning, a helicopter with Canterbury police SAR staff on board was expected to fly over open areas of land and near watercourses in the search area.
If Mr Cossey was not located, the search area would be extended to include the Bromley and New Brighton areas in Christchurch.
Mr Cossey was described as European, 187cm (6'1") tall, of a medium build with short brown hair.