Call the family court clerk in the county where the boy lives. Ask if any adoption procedings regarding him have been completed/initiated.
If they won't look up a juvenile's records, check under mom and step dad's names.
Check the service of process rules in the boy's state. You'll find them in the state's civil rules/rules of civil procedure, probably number 4. Under what circumstances is service by publication allowed? You can't do it in Washington unless you haven't been able to serve personally or by mail.
If service was improper, dad can challenge the adoption and have it rescinded.
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This is not legal advice and you are not my client. Double check everything with your own attorney and your state's laws.