California Code, Code of Civil Procedure - CCP § 413.30

(a)(1) If no provision is made in this chapter or other law for the service of summons, or if a plaintiff, despite exercising reasonable diligence, has been unable to effect service of the summons by any of the methods authorized under this chapter, the court in which the action is pending may, upon motion, direct that summons be served in a manner that is reasonably calculated to give actual notice to the party to be served, including by electronic mail or other electronic technology, and that proof of such service be made as prescribed by the court.

(2) A plaintiff seeking to establish reasonable diligence under this section shall set forth facts detailing all attempts to serve the defendant by each of the methods prescribed by statute, including facts demonstrating why each method was unsuccessful at every address or location where the defendant is likely to be found.