The AMBER Plan was created in 1996. It was named for Amber Hagerman who was abducted and murdered in Arlington, Texas in 1996. These alerts are carried on EAS, NOAA weather radio and some LED billboard signs and some SMS wireless text messages. In some states even the lottery LED displays are tied into the system. Online it's available at CodeAmber.org
Amber's family organized residents to contact legislators and media outlets about doing something. A reporter at 1080 KRLD-AM suggested they broadcast special “alerts” over the airwaves so that they could help prevent such incidents in the future. Rep. Martin Frost [D] drafted the Amber Alert bill. (For his good works, Tom DeLay redistricted him so severely he lost his seat in 2003.) President Bill Clinton signed it into law in 1996. The first trial runs of the amber alert system was at KRLD that same year.
Initially alerts were sent out manually. But by 1998 it was fully automated and by 2002 the FCC had officially endorsed the system. In 2002 the system had spread to Canada and international expansion has continued to the present day.