Farenthold was last seen in San Antonio, Texas sometime in April 1989. He had told his mother he was going to enter an unspecified drug rehabilitation facility in Florida and she purchased a plane ticket for him to travel there. He apparently never boarded his flight, however, and the ticket purchase was refunded to Farenthold's mother months later. Farenthold left behind his passport, clothing, motorcycle and car at his rented home. He has never been heard from again.

Farenthold is a member of a prominent Texas oil family and frequented the Corpus Christi, Fort Worth and San Antonio areas of Texas prior to his disappearance. There have been several tragedies among his loved ones: his twin brother died at age four after an accidental fall, and his older half-brother was murdered by a business associate in 1972. Farenthold's mother believes he is deceased. Many rumors have circulated about his disappearance, but none of them can be substantiated, and his case remains unsolved.