How can I get my husband to pay more child support?

You can file with the court a request for modification of child support.  You would file an Order to Show Cause (court form) requesting a modification of child support and a supporting declaration signed under penalty of perjury setting forth the facts in support of your request for modification of child support.  When you file the Order to Show Cause with the court, the court will set a date for a hearing on this issue.  You will also need to file a proof of service with your documents and serve your husband with the documents by mail.  You can use a court form proof of service or you can write your own proof of service.  If you write your own proof of service, it just says that you are over 18 and the attached documents were sent via first class mail unless specified otherwise to _________ (name and address of your husband) on _______ (date).  You sign and date at the bottom of the proof of service.  The date you sign should be the same as the date of mailing and the same date you file your documents with the court.

If you don't know your husband's whereabouts, he could be served by publication.  Service by publication is running a notice in the legal notices section of the newspaper for a set period of time.  The required period of time varies from state to state and the court clerk can tell you the required period of time for service by publication.  Even if your husband does not see the notice in the newspaper, it is still valid service by publication.