(CNN) -- More than 30 years ago, 6-year-old Etan Patz vanished from a Manhattan street on his way to a school bus stop. His parents never saw him again.
The case -- lately reopened by police -- riveted millions. It also changed the country.
"It awakened America," said Ernie Allen, president and chief executive officer of the National Center for Missing & Exploited Children. "It was the beginning of a missing children's movement."
The Patz case was the first of several high-profile cases that catapulted concern about missing children to the forefront of national consciousness.
Just weeks after Etan disappeared in May 1979, an attacker abducted the first of more than 20 children to be kidnapped and killed in Atlanta, stirring fear until police arrested a suspect two years later.
The cases received increasing news coverage in a fast-changing landscape that saw a proliferation of media outlets with growing interest in compelling visual images -- such as a heart-rending photo of a smiling child or video of parents pleading for their child's safe return.
The actual number of children who were kidnapped and killed did not change -- it's always been a relatively small number -- but awareness of the cases skyrocketed, experts said.
"Interest in the situation exploded," said Marc Klaas, whose 12-year-old daughter, Polly, was kidnapped and strangled to death in a 1993 case that also received intense news coverage.
"It really pulled the lid off of America's dirty little secret, the fact that children are being victimized in large numbers," he said Friday.
The cases also stoked fear, sparked awareness and prompted change from politicians and police.
In 1984, Congress passed the Missing Children's Assistance Act. That led to the creation of the National Center for Missing & Exploited Children.
President Ronald Reagan opened the center in a White House ceremony in 1984. It soon began operating a 24-hour toll-free hotline on which callers could report information about missing boys and girls.
Police officers also started to respond more quickly to reports of missing children, experts said.
After Etan disappeared, investigators tried what was then a novel technique to try to find him: They put his face on thousands of milk cartons, a technique that would become more common in the next few years.
Relatives and authorities also put the images of missing children on billboards and fliers distributed by mail.
Those more assertive efforts eventually led to the AMBER alert system, which broadcasts news about missing children on TV, radio, the Internet, mobile phones, lottery tickets and highway signs.
That system has helped save 554 children, the federal government says. Most of them were recovered after the first-ever White House Conference on Missing, Exploited and Runaway Children in 2002.
Before the dramatic increase in awareness of crimes against children in the 1980s, only a few high-profile
cases grabbed the public's attention.
Klaas points out that in 1873, after a 4-year-old Philadelphia boy named Charley Ross disappeared, authorities produced the first missing child flier.