During the war in Vietnam, Army Lieutenant Daniel Dawson’s reconnaissance plane went down over the Vietcong jungle. When his brother Donald heard the report, he sold everything he had, left his wife with $20, and bought passage to Vietnam. There he equipped himself with a soldier’s gear and wandered through the guerilla-controlled jungle, looking for his brother. He carried leaflets picturing the plane and describing in Vietnamese the reward for news of the missing pilot. He became known as Anh toi phi-cong—the brother of the pilot. A Life magazine reporter described his perilous search.
The Life magazine article in question was called "A Haunted Man's Perilous Search," from the March 12, 1965 edition of Life. Life is no longer in print but it is owned by time, and I'm still trying to find a back-issue of the article.
Time, however, did have a brief follow-up article on Donald's search, found here:
Californian Donald C. Dawson, 25, emerged from the jungle north of Bien Hoa airbase and reported that his reckless, obsessive search for his brother, Army Lieut. Daniel Dawson, was over after nine months—four of them as a Viet Cong prisoner. "They told me he was dead and gave me a flight vest he wore, and then they told me to go," said Don sadly. He never saw the grave, but the Viet Cong claimed they would tend it until Dawson could come back after the war to recover the body of his brother, shot down last Nov. 6 in a light reconnaissance plane. For Don, it was time to go home to his wife and four children in Costa Mesa, Calif.
The story really kicked me in the gut the first time I heard it related, and its one I'd like to write up in detail. I've found a couple more detailed but somewhat conflicting recounts of Donald's time in Vietnam here(from The First Marine Captured in Vietnam, by Donald Price) and here (from Honor Bound, by Stuart Rochester, Frederick Kiley).
In the meantime, more searching.