Photo

From left, Jourdan Dunn, Behati Prinsloo, and Cara Delevingne.Credit From left, Ian Gavan/Getty Images, Michael Loccisano/Getty Images for Fragrance Foundation and Juan Naharro Gimenez/Getty Images

In late July, Behati Prinsloo lent her voice to a chorus of protests when she took to Instagram to vent her outrage at the killing of Cecil the lion by an American hunter in Zimbabwe.

Ms. Prinsloo, who is from Namibia, is no household name, but the Victoria’s Secret model was quick to mine her demi-celebrity to assert her views on the web.

Joining her in shaming the hunter, Walter J. Palmer, was mega-model and actress Cara Delevingne, who branded him “a poor excuse of a human being” on Twitter.

They are but the latest in a troupe of increasingly media-savvy runway stars leaping onto the virtual soapbox of Instagram, Twitter or Facebook to share their politics and principles with fans. Many are making their names as self-appointed spokeswomen for any number of causes, burnishing their brands in the process and upending the perception that they are mere hangers for luxury wares.

Prompt to embrace her role as a walking billboard for a cause (and exploiting the chance to burnish her image), Jourdan Dunn took a break from posting snapshots of herself strutting in the latest in club gear, to pepper her Instagram feed with pictures of herself strolling the runway in a T-shirt, its legend proclaiming, “Fashion Against Ebola.”

Demonstrating that an image can speak volumes, the famously gap-toothed Lindsey Wixson posted a photo of herself on the cover of the current Thai Harper’s Bazaar tagged with the title “Woman Power.”

Not to be outdone, Ms. Delevingne asserted her championing of racial equality with an Instagram image of a placard stating, “Black Lives Matter.” Her message seemed to have the desired effect, triggering an outpouring of solidarity from her 17 million followers, and as tellingly, a gush from a fan who herself declared, “This makes me like you even more.”

Models’ lately found penchant for self-expression didn’t escape Karl Lagerfeld, who staged his spring/summer 2015 Chanel show in Paris last fall as a tongue-in-cheek mannequin uprising. Led by Ms. Delevingne, models took to the makeshift catwalk waving signs that demanded, “Divorce for All,” and “Match the Machos,” their faux protest signaling that activism is very much in vogue.

Some runway celebrities seem to be raising their voices just because they can. “Social media have given models a platform they didn’t have before,” said Sara Ziff, the founder of the Model Alliance, a nonprofit labor group widely perceived a catalyst for this latest wave of social engagement.

Instagram in particular, often referred to as visual Twitter, “has given these women the means to express their opinions, and to have some control of their image, their brand and their message,” Ms. Ziff said.

With that comes an expectation that these women act as role models and, as she pointed out, “that they have something to say other than what brand of lipstick they use.”

The savviest and most vocal, some with followings numbering in the millions, are championing causes far removed from the plight of poor Cecil and his lion kin, taking positions, albeit politely, on women’s issues, racial equality and gay rights, and, in rarer instances, declaring their support for political candidates.

Avery McCall, is using her rising status (she has walked for Alexander McQueen and Christopher Kane) to promote Hillary Rodham Clinton’s presidential run. “My goal is to number one, use my voice to engage a younger generation,” she told Teen Vogue in May. “I’m seeing a lot of room for sort of a blossoming social impact in the fashion world.”

Ms. McCall, 17, and others owe a debt to their predecessors: the highly vocal likes of Ms. Ziff, a former model herself, and to style-world luminaries like Christy Turlington Burns, whose advocacy for maternal health has arguably helped extend her brand and the longevity of her modeling career.

These days, a certain amount of banner waving is deemed not only acceptable but downright essential, a vital way for a model to reach the people who actually buy the clothes she parades.

“Our customers expect social commentary,” Paula Schneider, the new chief executive of American Apparel, said in an interview with Marie Claire magazine. “They expect it to be a part of their lives.”

And, she might have added, to reflect the thinking of millennials who have, as Jessica Goldstein wrote on the blogThinkProgress, shifted from detachment and irony to “sincerity, authenticity, and craft beer.”

Their appetite is avid. Millennials “want to know the full story behind anybody who is a public figure in their lives,” said Rob Gregory, an executive with WhoSay, a social media sounding board for celebrities and their followers. “They want to know the social stance of the people who give them their style cues. They expect them to have a point of view on important issues. These things now come with the territory.”

All of which goes toward explaining why certain influential agencies are grooming their charges to get vocal on the web. “We encourage our talents to be who they are,” said Vicky Yang, the marketing coordinator of the Society Management, which represents Kendall Jenner.

“We ask them to look at current events and not focus all the attention on what shoes they’re going to walk in next season,” Ms. Yang said.

The agency prompts models to take a stand on issues like world hunger, girls’ education, and racism. “We want these women to mold their own perspective and evolve the things they’re passionate about into a cause they want to pursue.”

Part marketing, that strategy is meant to underscore a model’s “authenticity,” she said. Still, there are limits. “We don’t want to censor, but we do issue guidelines as needed,” Ms. Yang said. “We urge our talents to draw people in without alienating anyone, and would likely steer them away from topics that are sensitive.”

Fans, in short, aren’t likely to find their idols campaigning for the right to life or taking up the crusade against child labor violations in offshore factories. (Why bite the hand that feeds them?)

And yet, not to take a stand, in some views, is to court (shudder) obscurity. “In this age of hashtag activism, you’re a bit out of the loop if everyone is tweeting ‘Black Lives Matter,’ and you don’t express sympathy or solidarity,” Ms. Ziff said.

“There is a sense that if you don’t have something to say, or more to offer, you’re just a pretty face,” she added.