LOS ANGELES - The crowds showing up to hear Bernie Sanders are not the result of pricey ads placed by his presidential campaign - in fact, the self-described democratic socialist from Vermont has spent very little to lure people to his rallies.

Instead, the eye-popping turnout is a testament to the power of social media and the promotional abilities of an alchemy of like-minded interests: progressive activists, labor unions and even comedian Sarah Silverman, who took to Twitter this week to let her 6.7 million followers know she'd be at a Sanders rally here.

The event at the Los Angeles Sports Arena Monday night drew an estimated 27,500 people - about five times as large as any crowd that's turned out for Democratic front-runner Hillary Rodham Clinton.

"Bernie always seems to be on the right side of history," Silverman told the boisterous gathering, noting that the 73-year-old was a civil-rights activist in the 1960s, supported gay rights in the 1980s and strongly opposed the Iraq war before most other Americans did.

All told, Sanders has attracted more than 100,000 people to his rallies in recent weeks, riding a wave of Facebook shares, retweets and old-fashioned word-of-mouth to become by far the biggest draw on the campaign trail.

Such turnout is no guarantee that Sanders will perform well in the crucial early nominating states - fellow Vermonter Howard Dean preached to similarly large and frenzied audiences in mostly liberal enclaves in 2003, only to collapse as the Iowa caucuses approached.

But it is drawing energy and attention away from Clinton (whose aides peg her largest crowd to date at 5,500), and exposing a lack of enthusiasm for her candidacy among some facets of the Democratic Party. And it is creating a network of small-scale donors and volunteers that could provide Sanders with the resources he will need to compete with the former secretary of state and first lady in the weeks and months ahead.

Roughly 28,000 people showed up for a recent Sanders rally in Portland, Ore. He drew 15,000 in Seattle; 11,000 in Phoenix; 10,000 in Madison, Wis.; 8,000 in Dallas; and 4,500 in New Orleans.

This weekend, Sanders will host a couple of town hall meetings in Iowa and attend events with other candidates; his campaign has not yet said where his next large-scale rally will be.

In Los Angeles, Sanders' campaign estimated that 27,500 people were jammed inside and outside the 16,000-seat arena - a figure impossible to independently verify. Nearly every seat appeared to be taken, and the arena floor was packed. Outside, thousands more watched the rally on large screens.

The throngs were greeted by Dante Harris, the leader of a local flight attendants union that had helped promote the rally.

"Did all of you make the trip out here on a Monday night because everything is going well for you and your family?" he asked.

"No!" the crowd roared.

Harris nodded and shouted back. "Workers' lives matter! . . . Black lives matter! . . . The truth matters!" Struggling to be heard over the ensuing ovation, he said: "We can build a movement with Bernie!"

The audience was noticeably more diverse than those at recent Sanders rallies in Portland, Seattle and other majority white cities - Los Angeles is majority-minority, with about 44 percent of its population Latino.

When Sanders came onstage, the cheers were deafening. His voice hoarse, the senator told the crowd, "This campaign is not a billionaire-funded campaign - it is a people-funded campaign."