California
Code of Civil Procedure CCP § 428.60
A cross-complaint shall be served on each of the partiesin an action in the following manner:
(1) Ifa party has not appeared in the action, a summons upon the cross-complaint shall be issued and served upon him in the same manner as upon commencement of an original action.
(2) Ifa party has appeared in the action, the cross-complaint shall be served upon his attorney, or upon the party if he has appeared without an attorney, in the manner provided for service of summons or in the manner provided by Chapter 5 (commencing with Section 1010 ) of Title 14 of Part 2 of this code.