How do you track down old friends from the military?

You can try Together We Served and of course there is always FB

Social media, Google.

it helps if you remember how to spell their last name and where they came from. I found my best friend that way. I contacted his home town Chamber of Commerce, they contacted him and the friendship started all over again. He gave me leads on another one and found him on the first try. There are now 5 of use who regulary visit and 1 that has passed