Police in Derry and the family of 27-year-old Sean Faulkner say they are becoming increasingly concerned for his welfare.
He was living at Great James Street in the city.
Originally from Antrim, Mr. Faulkner was last seen in Great James Street at 7 am yesterday morning.
The PSNI say Sean was wearing blue jeans, a dark puffa jacket and Nike trainers,
He is about 5ft 6ins tall, of stocky build with a shaven head.
The PSNI have appealed to Sean or anyone who knows his of whereabouts to contact Strand Road Police Station on the non-emergency number 101.