SA police seek help on missing man

South Australian police have appealed for public help in relation to a missing man believed to have been murdered.

Kenneth "Kenny" Camplin was last seen at a fast food restaurant in Adelaide's north in the early hours of December 27, 2013.

Police believe he returned home but went missing shortly after and was then murdered.

His body has not been located.

His vehicle and the receipt from the restaurant were at his home.

Major crimes inspector Greg Hutchins said on Wednesday that police believed Mr Camplin supplied small quantities of illicit drugs to friends and was a social drug user.

But his family and friends appeared to be trying to protect his reputation and had not been "completely forthcoming" about his involvement with drugs.

"A clear motive for Mr Camplin's murder has not been established," Mr Hutchings said.

A number of persons of interest had been identified and would be investigated further, he said.

Police have released CCTV footage of Mr Camplin taken hours before he went missing, which showed the clothes he was wearing.