The Facebook-themed horror movie “Friend Request” is so gloriously dumb that it is surprisingly a whole lot of fun.

This German/South African co-production, directed and co-written by Simon Verhoeven, takes the social networking site and mashes it up with message-board phenomenon Creepypasta to craft a horror flick that’s based in technology but rooted in a far more ancient evil.

Australian actress Alycia Debnam-Carey stars as popular college student Laura, beautiful, beloved and surrounded by friends and admirers at her picturesque seaside university. When she takes a misfit from her psych class, Marina (Liesl Ahlers), under her wing, her life starts to go completely haywire, especially when her new friend’s obsessive attention turns dark and needy.

Soon Laura’s besties are beset with terrifying hallucinations from the illustrations and animations that pepper Marina’s Facebook page. To make matters worse, Laura loses control of her own profile, which starts posting harrowing video of the campus deaths. Not surprisingly, Laura’s friend count plummets. And to think it all started with a simple friend request.

The film strikes the perfect chord for harmless horror movie fun: It’s littered with truly effective scares that will keep audience members jumping out of their seats, but it’s so silly, earnest and schlocky that laughter offers catharsis. All of the actors perform with a wide-eyed innocence and intense sense of melodrama that adds to the effect. It’s the perfect movie for the lost art of yelling back at the screen, “Don’t go in there!”

There are almost no rules to the frights of “Friend Request,” just that a friend request from Marina means imminent, gory, self-inflicted doom. Otherwise, demons, witches and wasps cavort with abandon, with only perfunctory reasons given as to the how or why.

The plot moves along swiftly, utilizing tried-and-true horror and teen genre character types and tropes to facilitate rapid comprehension of the story, before it descends into witchcraft, childhood trauma and black mirror rituals. But once it leaves its technological home base of Facebook, the film loses much of its steam, as we’re treated to that old chestnut of classic horror filmmaking — a final girl running away from a man with a knife.

“Friend Request” seems to be wanting to make some kind of statement. The terrain is ripe for commentary about our relationship to technology, the way we live our lives online. But any message gets lost in its rather sludgy climax.

It’s the highest praise to describe the final product as “a hoot” — the kind of midnight movie best seen with a large crowd laughing and screaming along, offering words of advice or encouragement to the naive characters on screen. It recalls the B-horror flicks of the ’80s and ’90s. If that’s your thing, it’s a good idea to accept this “Friend Request.”