You’ve spied the electronic billboard message on the interstate and maybe felt a chill as you did — "Amber Alert," then a car description, a license number. Who among us hasn’t at least taken a glance to the left and right to make sure we weren’t passing the suspect vehicle at that very moment?

But who among us would dare to follow such a car if we saw it? Yeah, we’d phone 911. But chase the vehicle, at a safe distance, to a service station? Try to peek in the tinted windows?

That’s the killer premise of "Amber Alert," an often effective, occasionally illogical thriller built on "found footage" of such a pursuit.

Sam (Summer Bellessa) and Nate (Chris Hill) are BFFs, Arizona 20-somethings who get Sam’s younger brother to videotape their audition tape for an unnamed reality TV show — probably "The Amazing Race." They’re bubbly chatterboxes who share their platonic hobbies and habits. And the unseen Caleb documents it all.

But their tape is now in police custody, we’re told, because on it they captured evidence of a crime. Driving down an interstate, they see an Amber Alert and spy the car listed on it — a gray Honda Accord hybrid, with matching license plate.

Sam is the one whose concern runs to worst-case scenarios. Nate frets over the time they’re "wasting" chasing this car (they’ve called the police), the meals he’s missing. It’s just a child custody dispute involving a divorced couple. He’s sure of it. "Do you not care if we lose them?" Sam shrieks. "Do you not care about little kids getting molested and murdered?"

Bellessa suggests there’s more to Sam’s determination, her willingness to take risks to help some child she isn’t even sure is in the Accord. Sam has the thoughtless immortality of youth, seemingly not thinking through what could happen to her if she confronts the driver of that car. Hill does a great job of playing the "just friends" guy, a timid pushover who will indulge the prettiest woman in his life simply to impress her, even if that tests their friendship.

As this lean little thriller drives along, tensions rise and tempers flare in the pursuit car. Nate, not wanting to get involved, is willing to believe the best, that the driver (Jasen Wade) looks like "a regular dude" and couldn’t be a child molester. "Reckless" Sam is hung up on the worst. By the time Sam is taking stupid risks, running up to the Amber Alert car at a service station, she’s hysterical.

But they’re not the only ones raising their voices.

For viewers, "Alert" is a real shout-at-the-screen picture. Where are the elusive cops? Why aren’t Sam and Nate calling and updating those cops with every turn the gray Accord makes? Why haven’t those cops tracked the license plate of the abductor, since that’s on their own Amber Alert notice board, and thus gotten to his house already?

In a thriller that’s as quick and short as "Amber Alert," some of those quibbles occur to you, briefly, as you watch it. But if you’re sucked into it, the worst of them won’t sink in until the closing credits roll.

We’ve seen ghosts and Blair witches and demons and zombies in this growing "found footage" genre. But "Amber Alert" brings a little something new to the form: the urgency of pursuit, risks with real-world consequences. And despite its many shortcomings in logic, writer-director Kerry Bellessa’s sharp execution almost makes up for them.

—Review by Roger Moore