Armadale Detectives are urgently trying to locate Cecil John Edgill and his five-year-old son, who they believe may be in danger.
Investigators said the pair were last seen in the Gosnells area on Sunday night.
Police hold urgent safety concerns for the boy, Romeo, who is believed to be with Mr Edgill.
Mr Edgill, 33-years-old, is described as having a medium build, approximately 180cm tall with brown hair and brown eyes.
Police urge anyone who see Romeo or Mr Edgill to call them immediately on 131 444.
Anyone with any other information regarding the whereabouts of Mr Edgill or Romeo, is asked to contact Crime Stoppers on 1800 333 000 or report online at crimestopperswa.com.au