How would you go about finding a Military friend you haven’t seen in many years?

That depends on how much, and what type of information you have on the friend.

● If you can remember their name and some military details, you can start right here by using the search box up above. When you get to the next screen, you can narrow the results down by member type, locations they served, military branch, etc.
● You can also try https://www.togetherweserved.com/ using the same type of information.
● If they were disabled and/or enrolled in VA healthcare, then you can reach out to the VA and have them forward a letter to the address they have on file.
● Reach out to various Veteran Service Organizations and see if your friend on is in their national directory.
● Don't forget the low-hanging fruit - search Facebook and other Social Media sites for any information.

COL Randall C. hit the nail.

But I would also try friends of friends - don't just search for your friend, search for anyone who may have known them. Maybe your friend is still in touch with someone else from the unit who you can reach out t.

classmates.com also has military classes and military units that you could try (but it costs money)
You can also try sites like peoplefinder or spokeo - but those, again, cost money.
And, if you are both rich and desperate, you can hire a PI.