It's extremely misleading. It's every time parents call the cops because they can't find their kid. Many are resolved within hours. Almost all are resolved peacefully. If your kid is a habitual runaway each time you report they didn't go to school or come home counts as one. After kids being assholes the number 2 cause is non-custodial parents.
About 1 in 10,000 aren't found or found alive. So 50 or 60 kids out of 84M that are under 18 at any given time are grabbed by predators or die whilst running away (hint OD)