While the military keeps records of service personnel who are on active duty, it does not track people who formerly served in the Marines. If the U.S. Department of Veterans Affairs has an address on record, it can usually forward a message for you, and some veterans' reunion organizations such as Together We Served offer Marine locator services.
Department of Veterans Affairs
The Department of Veterans Affairs cannot release personal information about a former Marine for privacy reasons. However, it can forward a message from you, provided the VA has a current address on record. To use the VA messaging system, write a letter to your friend and place it in a stamped, unsealed envelope. Next, write a letter to VA describing the person you are trying to find; include the veteran's service details if you can. Put both letters in another envelope, and deliver it to your nearest VA regional office. The VA will mail your letter to the address it has on file. It is then up to your friend to contact you.
Together We Served
Together We Served reunites more U.S. veterans each year than any other organization, so if you served in the Marines and are looking for a former buddy, this is a good place to start. You'll need to create a profile to make contact with other veterans. From the home page, click the "Join Now" button, then enter your details. You'll be taken to a profile page where you can fill out your units or duty stations, with associated time frames, and from there view a list of old service friends.
Vet Connect – also known as Google for Veterans – was specifically created to help veterans and their loved ones connect with each other. It's free to sign up, which you can do using your Google Plus account. Once on the platform, you'll be asked to submit your service experiences, and Google will look up former Marines with similar service details. If your friend is listed, you can add him to your circles and send a private message through the Google Plus platform.
Military.com Buddy Finder
Military.com holds over 20 million records for current and former members of the military, including information obtained from Military.com membership lists and the Department of Defense personnel records. To start your search, simply fill out the form on the Buddy Finder home page. Provide as much identifying information as possible such as full name, pay grade, job code and approximate age, and then hit "Find Buddy." The website will look up former Marines for you.
USMC Military Reunions
The Marine Corps is not able to assist in locating former Marines, but its website does contain links to special interest organizations that might be able to help you. Simply click on a link for details. The Marine Corps' sister website, Marine Corps Community Services, contains lists of past and upcoming reunions and similar veterans' events. The site lists contact information for the event organizers, who might provide some favorable information.