“Reasonable efforts" to locate a spouse is a standard used in court to ensure that an individual has taken sufficient steps to locate their spouse before proceeding with an action such as divorce via service by publication.
What counts as "reasonable" can vary depending on the specifics of the case, but generally, it involves the following actions:
 Contacting Friends and Family: You should attempt to reach out to known friends and relatives of your spouse. They might not provide you with the information due to loyalty, privacy, or other reasons, but this attempt should be documented.
 Checking Last Known Address: If you have a recent address for your spouse, visiting or sending a letter to this address may help establish contact.
 Online Research: This can include searching through social media platforms such as Facebook, LinkedIn, Twitter, or Instagram. Also, a simple Google search of your spouse's name could provide helpful information.
 Contacting Previous Employers: If you know where your spouse used to work, contacting those employers might provide some leads. They may not be able to share much due to privacy laws, but knowing that you tried will count as a reasonable effort.
 Public Records Search: You can search public records that might have recent information about your spouse. This could include property records, voter registration records, or court records.