If you live in Southern California and attend a few concerts each year, you’ve probably seen Alex Napolin’s ads on Facebook. The sponsored posts seek out anyone who attended or lost a loved one at the Route 91 Harvest Festival in Las Vegas last year, where a single a gunman fired on the event, killing 58 people and leaving 500 injured.

“TIME IS RUNNING OUT!” says a Facebook ad from Napolin, a personal injury attorney from Claremont, California. “If you attended the Route 91 Harvest Country Music Festival, you may be eligible for financial compensation.”

Napolin is one of several attorneys using Facebook to find plaintiffs for a class-action lawsuit against the estate of shooter Stephen Paddock, as well as MGM, which owns the festival site and Mandalay Bay hotel, and concert promoter Live Nation. The Oct. 1 attack, the worst mass shooting in modern American history, could result in a $1 billion payout, mostly paid by MGM and Live Nation, attorneys claim.

While using advertisements to find plaintiffs for class action lawsuits is nothing new — think of the late night commercials seeking victims of medical malpractice or asbestos exposure — the use of targeted social media campaigns represents a paradigm shift in the legal world, where viewers can tag friends (and potential clients) in the comments section and easily share the post with others.

“Facebook is a good way to market because it’s a good way to get people together,” Napolin told Amplify in an interview. “If it wasn’t working I wouldn’t be doing it,” he said, noting that he’s not the only attorney looking for clients on Facebook. Personal injury Attorney Chad Pinkerton is also using the service, running Facebook Live Q&As where he talks about the 1,500 clients he represents in the Las Vegas case and shares updates on the class action lawsuit. Pinkerton said he is on a lead trial group of attorneys who will ultimately file the master complaint in the case.

“We have a lot of people that were victims,” Pinkerton said on a recent Facebook live posting. “The police report that 22,000 were at the concert that night,” he explained, adding “whoever was there was a victim and could have a claim in this lawsuit.”

Napolin said the Facebook ads aren’t just about the suing MGM and Live Nation, noting he’s helped a number of clients receive money from victims funds and GoFundMe campaigns.

“I know countless people that were there,” he said, noting that he is passionate about the case and wants to help the victims. His partner Catherine Lombardo has attended all the hearings on Route 91, he said, and has appeared on Fox News several times to talk about the case.

Napolin won’t say what keywords he uses to target the ads — “I can’t tell you specifically how I construct the ads, that’s proprietary information, but obviously they work,” he explained.

“We’ve gotten a lot of negative comments about the Facebook ads, it’s been a hard run with those,” Napolin said. “There’s negative comments, but there’s also positive comments. There’s people that don’t quite understand what everyone went through.”

Napolin said he used a similar strategy to find plaintiffs in a case against Children’s Dental Group last year, with 58 claims eventually filed against the city of Anaheim, alleging water supplied to the clinic was contaminated and led to infections in young patients undergoing root canals.

Napolin in front of Children’s Dental Group

“I didn’t get any negative publicity for that or negative comments with people saying I’m just trying to make a buck,” he said. “The whole thing has been difficult. It’s such a horrible tragedy and I’ve spoken with so many people and hearing their stories has been very hard.”

He said the Route 91 case “is not your typical class action where we’re just counting up the dollars a credit card company owes,” and added “every story is very intense and people are really hurt. Even those who attended the event but weren’t shot are affected,” noting some had to miss work or pay for therapy, while many are reliving the attack and suffering from PTSD.

“Some can’t go into public places,” he said. “And I’ve got to give a lot of emotional support to the clients and that’s very difficult personally, especially with this case which is particularly painful and sad.”

Napolin even operates a questionnaire on his site that first asks if potential clients purchased their tickets, and whether they have proof of their attendance either through receipts or wristbands. It also asks questions like “Did you see anyone get shot?” and “Did you see any bodies on the ground that had been shot?”

So far, five lawsuits have been filed representing 450 victims, mostly in California. A judge still has to decide if the case takes place in Nevada where the shooting took place, or in California where many of the victims live.