As the commotion surrounding Twitter’s new ownership leads some users to consider moving to smaller social-media sites, Tumblr is pitching its free-to-use microblogging service as a welcome throwback to the early internet: a place where people can be as weird, creative and nerdy as they like by posting and reposting media from photographs to poetry. 

Renewed interest could write a comeback story for a platform that once loomed large in the internet zeitgeist but has struggled to turn its popularity into cash.

Founded by

David Karp

in 2007, Tumblr quickly became known for the quirky, often inside-joking nature of its content and its anticorporate tendencies. It steadily accrued bloggers for five years and announced its first advertising product in 2012. 

Online media brand Yahoo acquired the platform for $1.1 billion a year later, setting its sights on drawing in advertisers with Tumblr’s young, engaged user base. But the company struggled to execute its plan and in 2016 wrote down the value of the acquisition by $712 million. Wireless company

Verizon Communications Inc.,

which bought Yahoo in 2017, saw Tumblr users nosedive when it banned adult content, including nudity, in 2018.

Tumblr’s latest owner, Automattic Inc., is trying again to attract advertisers even as it pursues new revenue streams. But marketers aren’t convinced, concerned that the idiosyncrasies that continue to define Tumblr make it a complicated place to advertise, according to media executives. 

“I wouldn’t say it’s something that clients are asking about or really have on their radar as of today,” said Prerna Talreja, managing director of digital activation at media agency Crossmedia Inc.

History repeats

When Yahoo bought Tumblr, the deal wasn’t welcomed by a vocal number of the platform’s users, some of whom worried that Yahoo would kill what they loved about the site in the name of ad revenue. But marketers also proved lukewarm to the new ownership, partly because the offbeat nature of Tumblr’s content meant companies found it hard to seamlessly slot their ads into users’ feeds, according to Tamara Littleton, founder and chief executive of the Social Element Ltd., a social-media-management firm. 

“Tumblr has always been a notoriously challenging place for brands to break into,” Ms. Littleton said. 

The platform remains as idiosyncratic as ever, Ms. Littleton said. Tumblr users in the past month have depicted anthropomorphized versions of the Tumblr and Twitter logos, for example, having a quasiromantic relationship. 

“If a brand is looking to embrace the weird, then it’s a great place to be,” said Greg James, global chief transformation officer at advertising communications firm Havas Media Group. “But frankly, most brands aren’t trying to embrace the weird.” 

The corporate struggle to blend in 

Tumblr today offers advertising formats including branded takeovers of the site, sponsored posts and standard banners that can be bought through automated ad systems. It continues to run Creatrs, a program established in 2015 to pair Tumblr artists with advertisers. And in April, it introduced Tumblr Blaze, which offers users, including brand accounts, wider exposure for their posts.

Advertisers that create custom campaigns using the parlance popular among Tumblr users to appeal to particular communities usually see the best engagement, according to Tumblr’s chief marketing officer, Matthew Ryan. 

Some of the most active advertisers on Tumblr are movie and television studios that create Tumblr campaigns for die-hard fans of genres or series, Mr. Ryan said.  

Still, the effort required to craft a bespoke campaign for Tumblr can be off-putting for some clients looking to reach consumers outside of a niche interest group, Crossmedia’s Ms. Talreja said. 

A company spokeswoman said the freedom Tumblr offers might seem daunting, but that it can lead to more creative campaigns that go beyond a typical online ad unit. 

Diversified revenues, new moderation practices

Tumblr has begun to seek revenue beyond advertising, selling subscriptions to some creators’ content and add-ons that users can gift to each other, including ad-free browsing and “Dashboard Crabs”—pixelated crustaceans that crawl across users’ screens when a button is pressed.

 Nevertheless, the company hasn’t given up on advertisers. 

“Everyone on the [ad sales] team is working really, really hard right now,” Automattic Chief Executive

Matt Mullenweg

said.

Tumblr doesn’t let advertisers target consumers with the granularity that technology company

Meta Platforms Inc.

does on Facebook and Instagram, for instance, Mr. Mullenweg said. 

It does offer a brand-safe environment, even after Automattic reintroduced some nudity to the platform earlier this year, he added. 

The company in September began requiring posts featuring adult content, including sexual themes and violence, to be labeled so they are not shown to users under 18 years old or people who don’t want to see them. Paid ads don’t appear next to posts labeled mature unless the advertiser has specifically opted into them.

And Tumblr offers marketers access to so-called Gen Z consumers, who make up just over 54% of its users, he added.

Tumblr’s success with advertisers will come down to whether it can grow its users, Crossmedia’s Ms. Talreja said. 

Mr. Mullenweg wrote in a tweet that downloads of the Tumblr app had increased 58% on

Apple

devices and 57% on Android devices in the first week of November, days after Mr. Musk acquired Twitter. 

Tumblr declined to disclose user figures. Around 18.4 million unique users visited Tumblr via the website or app on desktop and mobile in October, down from 23.2 million in the same month the year before, according to media-measurement firm

Comscore Inc.

In contrast, Twitter in the second quarter of the year said it had 237.8 million monetizable average daily active users, while Meta Platforms in October reported 2 billion monthly active users on Instagram and 2.96 billion on Facebook. 

“Ultimately, as advertisers, we want to be where people are,” Ms. Talreja said.

Write to Katie Deighton at katie.deighton@wsj.com