Due process-requirements-for-service-of-process-on-foreign-defendants

QUESTION PRESENTED In these federal cases Plaintiffs could not locate Defendant in California for personal service of process, because at all times Defendant was a resident and citizen of China. Plaintiffs had reasons to know or suspect that Defendant was in China, but made no effort to locate her there. The District Court permitted either substituted service in California, or service by publication in California, pursuant to California law under Federal Rule of Civil Procedure 4(e)(1). This resulted in default judgments against Defendant. When Plaintiffs have reason to believe that Defendant may be located and served in a foreign country, do the Due Process Clauses of the Fifth and Fourteenth Amendments require Plaintiffs to conduct a reasonably diligent search for Defendant in that foreign country before substitute service or service by publication are permissible?