Knox disappeared from El Paso, Texas on February 14, 1987. She attended a Valentine's Day party at Veterans Park in the northeast part of the city. Witnesses saw a young man driving a small truck pull up at the entrance to the park and speak to Knox. She disappeared a short time later. Someone saw her walking on Chaparral Street in Chaparral, New Mexico at 3:00 a.m. the next day. Knox lived with her family on Byrum Street in Chaparral, which is about 25 miles from El Paso. She has never been heard from again.

That same year, several other females disappeared from El Paso, and most of them were later found murdered and buried in the desert. The victims were all small, slender young women in their teens and early twenties. Knox and two other females, Melissa Alaniz and Cheryl Vasquez, are still missing.

David Leonard Wood, a serial rapist who was paroled in January 1987, was later convicted of murdering six of the El Paso victims, though he maintains his innocence to this day. He resembles the man Knox was seen speaking to just before her disappearance, he had lived in Chaparral off and on, and he apparently knew Knox slightly. He was sentenced to death in 1993, but his sentence remains under appeal, as his lawyers allege he is mentally retarded. The murders of El Paso girls and women stopped after Wood's October 1987 arrest for rape. He has not been charged in connection with Knox's case and it's unclear whether he was involved.

Knox was athletic in 1987 and enjoyed sports and horses. At least one of her friends believes she's still alive, but there is very little evidence as to her fate. Her father is now deceased. New Mexico police are investigating Knox's case.