Five men have been arrested on suspicion of murdering a man not seen in a month.
Michael Wheeler, 37, from Yeovil, has not been seen since 24 August and his car was recovered last week after being found in the town.
Mr Wheeler has not been home or been in touch with family or friends.
Avon and Somerset Police also said he has missed a number of regular appointments.
Five men are currently in police custody after being arrested on suspicion of murder.
They are aged between their late teens and late 30s, the force said.
A sixth man who was arrested last week remains on bail.
Detective Chief Inspector Lorett Spierenburg said: “We have been keeping an open mind over what has happened to Michael, who has now not been seen for a month, but we can confirm this is being treated as a murder inquiry.
“Arrests were made last week to enable us to question several individuals while under caution to understand if they knew anything that could help us locate Michael.”
She added: “Detectives will be questioning all five men as part of our ongoing efforts to establish what has happened and whether any criminal offences have occurred.”
She said Mr Wheeler’s family were being supported by specially-trained officers.