Police declare SA man's disappearance a major crime

Police have declared the disappearance of 23-year-old South Australian man Paulo Gorge Miranda a major crime.

Mr Miranda was last seen by a friend in Adelaide a week ago.

Police say his mobile phone is off and his car has been found burnt-out north of Adelaide at Port Prime.

Detective Inspector Doug Barr says another cause for concern is that some of Mr Miranda's associates are involved in the illicit drug trade.

"He's usually in regular contact with his family and friends and no contact has been made since that time," he said.

"We've had mounting fears over the course of the last week and it's come to the point now where we are concerned for his safety and welfare."