Adventure - 2 brothers in jungle and one goes missing

[Tegenn]

2 brothers live in the jungle, near a river (I think) and the older brother goes missing one day, so the younger brother follows the river to try and find his brother.

Probably published in the 60s or early 70s at that latest, but likely before - my dad read it when he was young and he was born in 1961.

Thank you to anyone who can help!

[Kris]

Tegenn, I moved your request to the Unsolved folder because you're looking for a specific book.

[Tegenn]

I found the name of the book: Riverboy (based on the adventure on the Amazon by Ralph Herrmanns).