Helicopters and local volunteers have joined police in a search for a seven-year-old boy who disappeared from camping ground south of Adelaide.

Police say the boy wandered off from his family as they picnicked in the Deep Creek Conservation Park around 1.15pm (AEST) on Saturday afternoon.

Police briefed around 40 SES and Country Fire Service volunteers who joined the search at around 7am on Sunday.

Two search and rescue helicopters will also be used in the hunt.

The boy was last seen wearing a polar fleece red hooded top and brown tracksuit pants.