Family of a 64-year-old man, who is missing from Sydney's south, fear for his welfare after he was involved in a car crash and told a friend he was deteriorating.

Police are asking for help to find him.

Police are concerned for the welfare of Paul Parkinson, who has been missing since Monday.

Police said Paul Parkinson was involved in a minor crash on Monday afternoon.

Friends and family last heard from him about 6.30pm on Monday.