Born 10-30-1971 Searching for birth family

Male YOO Sung Wook born 10-30-1971 in Seoul City Korea, Father Kyung Ki YOO Deceased 11-1975 and mother placed him with Grandmother Ja Deuk LEE after passing of father then placed for adoption. 2 siblings were either placed for adoption as well or raised by other family members. Korea Social Services, Inc. handled adoption. YOO Sung Wook was placed with them on July 1976. Brother Sung Soo born in 1969 and Sister Jung Hyun born in 67. Mother In Sook KIM born in 1947. Any help would be greatly appreciated.