Over seven years, the dark, camp teen drama has given its huge fanbase hints, spoilers and extra OMG moments online; it even lets them write plots. Is this the future of television?

Back in 2010, the teen TV landscape was dominated by the brooding One Tree Hill, the privileged otherworld of Gossip Girland 90210s LA melodrama. So when Pretty Little Liars debuted that summer, it barely cast a shadow. No one could have guessed that seven years on, as it bows out for good, the show would have smashed multiple social media records and be a loss of epic proportions for its fans worldwide.

Based on Sara Shepards eponymous YA series, Pretty Little Liars traced the lives of a high-school foursome studious Spencer (Troian Bellisario), sporty Emily (Shay Mitchell), fashionista Hanna (Ashley Benson) and alt-girl Aria (Lucy Hale) as they were terrorised by a mysterious assailant known only as A, following the disappearance of their best frenemy Alison (Sasha Pieterse). With one text, everything changed: Im still here bitches, and I know everything.

Wed had The OCs Marissa and substance abuse, Awkwards morbid humour and forbidden trysts in every primetime YA show going, but PLL kicked that darkness up a notch. Students had affairs with teachers, were sectioned and framed for murder, set upon in police chases and came back from the dead. As the boyfriendsand the bodies piled up, and consecutive cliffhangers pushed the mystery in ever-more fantastical directions, a compelling story of female friendship emerged. The pace was exhausting, perhaps, but PLLs fans were devoted.

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Its the perfect storm Pretty Little Liars. Photograph: Eric McCandless/Getty

Marco Sparks, one half of the US podcast Bros Watch PLL Too, has been a die-hard stan from the get-go. Despite the implausible storylines, he says, PLL is, at its core, a kaleidoscope of a mirror which is to say thoroughly relatable.

When the show is at its most ridiculous, dealing, say, with the machinations of an omnipotent cyber ninja, it still features characters struggling with mental issues in a realistic way, he says. It works because its the perfect storm of embracing all of that and throwing it into a blender of camp and ridiculous. Its Valley of the Dolls, Shirley Jackson and Alfred Hitchcock all wrapped up in one.

PLL Theories, a popular Twitter account for fans created in 2015, live-tweets each episode and dissects theories. The accounts admin describes how Twitter helps people connect with TV like never before, and particularly to this show. Im always tweeting pictures of my favourite ships [relationships] and video edits of great episodes, they say. It grips you; it wont let you go.

The series was certainly a social media trailblazer: on more than one occasion it held the title of the most-tweeted about television finale ever, smashing 4.5m tweets in one day in 2015. Lucy Hale, who plays Aria, says it was one of the first shows to use hashtags (#Spoby, #Haleb, #PLLGameOver) and actively interact with fans on its community pages after OMG moments. A case in point: their on-air promo campaign, challenging fans to tweet #CeCeIsA 300,000 times to unlock an exclusive video, was smashed in a matter of hours. Meanwhile stars and staff alike would drop hints about future plot developments on Twitter. According to I Marlene King, the shows executive producer, the writers room took heed of fans likes and dislikes, particularly when it came to relationships, like reuniting Hanna and bad boy Caleb.

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Its Valley of the Dolls, Shirley Jackson and Alfred Hitchcock all wrapped up in one Pretty Little Liars. Photograph: Warner Brothers

Of course, PLL wasnt the first show to see fans expand the fictional universe through transmedia storytelling. But where Dawsons Creek and The OC had spin-off books and Myspace hubs, the Liars wove social networks right into the fabric of the show, involving the fans even further. Villains set tasks and taunted the girls via texts, mail and apps. Each seasonal cliffhanger gave way to an avalanche of forum storming. A rotating faction of the cast would watch each weekly episode and report back on Twitter. Theres a democratising feel to that engagement, says Sparks. It allows viewers a sense of buy-in. In other words: if youre not on URL, youre not getting the full PLL experience.

Fan-fiction is another major part of the PLL experience. Popular fan-fic writer JennasSunglasses writes extensively, as do many others, about Emison: the lesbian relationship between Emily and Alison. Their storyline just seem so precious, she says. Her particular focus is on the girls younger years: Weve only gotten (Emison) in flashbacks, and Ive always wondered what wouldve happened if Alison returned Emilys feelings from the beginning, she says.

Looking at these creative spin-offs, character role-playing Twitters and impressively detailed YouTube theory videos, its clear that the PLL universe lives and breathes beyond the screen. Visceral and smart, Pretty Little Liars is the Buffy, the Veronica Mars, the Mean Girls of its time, and its fandom will stay devoted long after the camera backs away from this small, strange town of Rosewood, Pennsylvania.

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