Carson Shephard was last seen in the Afton Bridgend area of New Cumnock at about 7.20pm on Sunday (September 19).
He is about 3ft 6ins, has short dark brown hair and is of slim build. He was last known to be wearing dark blue jeans, a t-shirt and a black top.
The police helicopter, marine and dog units, and Scottish Fire and Rescue Service water support unit are all involved in looking for the child.
Since Carson was reported missing on Sunday evening, the local community has been helping police officers in the area.
Anyone who has any information or may have seen Carson, or know of his whereabouts, is asked to call Police Scotland on 101, or 999 in an emergency situation, quoting incident number 3162 of Sunday September 19.