> reporter: on a warm windy evening in september, 23 years ago, desiree's mother, 19-year-old samantha hopperrandmother debbie's house before driving off with her 2-year-old daughter, kourtney. >> she always said she loved me. and so she left. she never came back. and they just went on and on and on. i sat on my front porch watching the road. she never come back. >> reporter: samantha disappeared without a trace. despite a lengthy police investigation that went on for two decades there were no signs of her or her young daughter, kourtney. vanished and missing for more than 23 years. >> i feel that so many missing person reports, that every time you do that, you have to give them a picture. and i don't have no pictures left. i don't have nothing. >> reporter: despite the pain, despite the anguish, samantha's case tragically is anything but unique. every year, more than 600,000 people go missing in the united states. it's been called the nation's silent mass disaster. a trend that presents an alarming reality for families in law enforcement. hundreds of thousands of people to search for across