(Washington Post) - Pretend for a moment that you are walking through your neighbourhood and notice a line of people wrapped around the block outside a newly opened restaurant.

Local food bloggers have not written about the venue, so you assume the trendy-looking crowd must be the result of contagious, word-of-mouth buzz.

There was a time when that may have been undoubtedly true - when you could trust that a crowd of people was, in fact, a naturally occurring mass of individuals.

But that time may be passing, thanks to Surkus, an emerging app that allowed the restaurant to quickly manufacture its ideal crowd and pay the people to stand in place like extras on a movie set. They have even been handpicked by a casting agent of sorts, an algorithmic one that selects each person according to age, location, style and Facebook "likes".

They may look excited, but that could also be part of the production. Acting disengaged while they idle in line could tarnish their "reputation score", an identifier that influences whether they will be "cast" again. Nobody is forcing the participants to stay, of course, but if they leave, they will not be paid - their movements are being tracked with geolocation.

Welcome to the new world of "crowdcasting".

Surkus raises new questions about the future of advertising and promotion. At a time when it has become commonplace for individuals to broadcast polished versions of their lives on social media, does Surkus give businesses a formidable tool to do the same, renting beautiful people and blending them with advertising in a way that makes reality nearly indiscernible? Or have marketers found a new tool that offers them a far more efficient way to link brands with potential customers, allowing individuals to turn themselves into living extensions of the share economy using a structured, mutually beneficial transaction?

The answer depends on whom you ask.

Mr Stephen George, Surkus' 30-year-old chief executive, said he considers his app an online matchmaker, one that pairs companies with the people who want to hear from them. If successful, he said, Surkus threatens to disrupt the expensive role that promoters and public relations firms have traditionally played in advertising and brand-building.

"So many companies know their core demographic, but they don't know how to get a hold of those people," he said. "They hire promoters and marketers and PR agencies to connect, but it's a one-sided interaction that involves blasting out a message to get people engaged, but they don't necessarily know if that message is being received."

Not everyone, however, is convinced that Surkus - which makes it easier for promoters and marketers to filter crowds according to people's attractiveness - will improve that reception.

"I understand the need for quick results and attendance and that sometimes brands need people lined up at their door," said Professor Kerry O'Grady, who teaches courses on public relations at New York University's School of Professional Studies.

"Okay, you have a bunch of pretty faces at a party, but what does that do? It's not going to do anything if they just want to get paid to party and have no attachment to the brand itself."

Mr George, a Chicago native, got his start working with Groupon as a sophomore at DePaul University. He went on to make millions from the company's stock before investing US$250,000 in Surkus in 2015.

The company's tagline: "Go out. Have fun. Get paid."

Mr George said the company has amassed 150,000 members in Los Angeles, New York, Chicago, Miami and San Francisco. Anyone can download the app. The members are of all ages and backgrounds, he said, noting that people are drawn by the chance to be social and get paid.

After quietly launching two years ago, Surkus members have attended 4,200 events for 750 clients, including big-name brands, hospitality groups, live-ticketed shows, movie castings and everyday people who want to throw a party.

Mr George said users can be paid as little as US$5 (S$6.80) and as much as US$100, though the average for most events is between US$25 and US$40. Prolific users, he said, can earn as much as US$4,000 a year. And Surkus takes a portion of the client's budget for each event.

The app is supposed to help with these transactions.

Once an event has been scheduled, Surkus' algorithm sorts through users' profiles using the client's desired search criteria. For example, a gaming company throwing a launch party might ask Surkus to find men and women aged 18 to 32 who like comic books, day parties, dance music and the company's product.

Once potential attendees have been identified from Surkus' user profiles, the app sends "availability requests" to users' phones.

Participants are paid within 24 hours via PayPal. During events, participants are asked to remain discreet about the origin of their invitations. Oftentimes, women are paid considerably more than men.

Ms Caroline Thompson, 27, a contributing writer for Vice, said she downloaded Surkus and attended an event last year at a Chicago club full of "finance bros" on a Thursday night. "It was a little weird that probably 80 per cent of the women at the club were there because of the app," she said.

She said she was paid US$40 to attend the event.

Prof O'Grady called the system "scary" and said it raises ethical questions for companies that turn to the app for crowds. "Good PR is all about transparency," she said. "But in this case, you're telling people to be discreet, but you're also telling us the events are organic and that people want to be there, and that's not okay."

Mr George rejected the idea that Surkus allows brands to create fake events that manipulate consumers. "We want to know as much as possible about you, so we can make sure we're on target with your interests and what you love to do, so that you just can't say no to an invitation," he said.

Entertainment companies are not the only ones turning to Surkus for crowdcasting. Mr George said a research company recently used the app to find 750 people to fill movie theatres in Los Angeles and New York to compare how reactions varied from city to city.

In Los Angeles, Surkus has allowed one up-and-coming comedian to fill shows and refine material.

The comedian requested that his name and gender be withheld from publication because of fear that using the app would tarnish his professional reputation. At many comedy clubs, filling seats is a prerequisite for performing.

The comedian used to be desperate, passing out fliers and asking homeless people to attend so that the performance could go on.

Now, the comedian turns to Surkus. "Initially, I thought my jokes would appeal to educated white hipsters," the comedian said. "Now I've realised, 'Oh, wow, my act is appealing to Hispanic women and men in their 50s and old people - like, we're talking people in their 70s."