The disappearance of a "well-loved" man is "highly out of character", one of his friends has said.
Michael Cullen (33) was last in contact with his family on Tuesday at around 2pm.
From the North Circular Road area in the north of Belfast city he is described as a well-known beatbox performer who has played in London and Dublin.
Friends have organised through a Facebook group co-ordinated searches and appeals. Teams took to the Cave Hill on Thursday to help with the search effort.
Rory Girvan, organiser of the group, said they "optimistic" during a search of the Cave Hill on Thursday afternoon.
He said Michael was "well-loved" highly intelligence. He said he was probably Ireland's best beatbox performer and his disappearance was "highly out of character".
Police said his family were growing increasingly concerned and have appealed for anyone who has seen him to get in touch and they have also deployed drones to help in their search.
Michael is 5"11 tall with dark hair and beard. He was wearing a green puffa jacket, grey jumper and black trousers before he went missing.