LOS ANGELES — The critics have spoken. Here’s what more than a few have to say:

“Scariest movie of the decade.”

“Scariest movie of my life.”

“Scariest movie of our time!”

For Hollywood studio flicks, such raves usually are no more than icing on top of a marketing campaign that cost tens of millions.

For “Paranormal Activity,” the raves are the marketing campaign.

The comments above, repeated over and over again in various contexts on Twitter and Facebook — along with other online fan buzz — propelled the micro-budgeted horror movie to a $7.9 million weekend in just 160 theaters.

That’s a colossal average of $49,379 a theater, compared with $11,429 in 3,000 theaters for “Couples Retreat,” which debuted as the weekend’s No. 1 movie with $34.3 million.

“Couples Retreat” has stars — Vince Vaughn, Jon Favreau, Kristen Bell, Kristin Davis — plus the traditional mammoth studio sales push — one that included TV spots, billboards and a chic junket for Hollywood reporters on Bora Bora.

“Paranormal Activity” mainly has just its fans — a legion growing by the minute as more and more people post their thoughts.

Distributor Paramount Pictures so far has spent only a couple of million dollars promoting the movie, a fraction of the marketing budget for big releases. Most of that money has gone into its Web site and to set up screenings to build the buzz.

“This movie doesn’t lend itself to a big, giant marketing campaign. This movie is an old-fashioned word-of-mouth movie,” said Rob Moore, Paramount vice chairman. “By and large, at today’s production budgets, it’s really hard to say, ‘All right, now we’re going to rely on the audience and their word of mouth to make it work.’ Not when you have tens of millions of dollars in production costs invested in the movie.”

The studio has only a pittance invested in “Paranormal Activity.” Shot by writer-director Oren Peli for a reported $15,000, the movie was acquired by former Paramount partner DreamWorks at 2008’s Slamdance Film Festival.

The original idea was to reshoot the movie, putting more money and gloss into the documentary-style fictional tale of a couple tormented by strange phenomenon and apparitions.

But Paramount decided Peli’s raw little fright film could stand on its own. The studio trimmed the movie a bit and punched up the ending, then tried to figure out the best way to hook fans.

In keeping with the movie’s do-it-yourself indie spirit, Paramount started with midnight-only screenings in 13 cities, then let the online community decide where the movie would play next.

Over the second weekend of midnight shows, “Paranormal Activity” expanded to 20 more markets where it got the most requests from a Web site the studio had set up. Fans continued to vote, deciding the movie’s next destinations as it went into all-day release in 46 markets this past weekend; the studio plans to continue rolling the movie out to more theaters based on what towns request it the most.

The fan base has grown exponentially as more people saw the movie, then jumped online to write about it

“On the social-networking sites, everybody’s talking about how freaking scary this movie is,” said Paul Dergarabedian, box-office analyst for Hollywood.com. “This does not happen every day. This is literally capturing lightning in a bottle.”

Internet hype has become part of every movie’s marketing plan, but online buzz generally is a supplement to traditional advertising.

Another indie horror tale, 1999’s “The Blair Witch Project,” became the biggest hit ever discovered at the Sundance Film Festival as months of online chatter pushed it to a $140 million haul.

Preceded by similar Web patter, 2006’s “Snakes on a Plane” wound up fizzling, fans deciding it was more fun to sound off about the movie online than to actually see it.

With a combination of Internet buzz and cryptic advertising, Paramount created an aura of mystery around producer J.J. Abrams’ monster movie “Cloverfield,” turning it into a solid hit last year.

Paramount is adding hundreds more theaters this Friday, a critical weekend that will help determine if “Paranormal Activity” graduates from impressive indie success to full-blown phenomenon.

Could “Paranormal Activity” be the new “Blair Witch,” riding online mania to join the $100 million hit club?

“That would seem highly improbable, since it hasn’t happened this decade,” Paramount’s Moore said. “I certainly wouldn’t attach a goal at that level, but it certainly has turned into a major success, and the next several weeks will determine what level of success it’ll reach.”

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