Yahoo says that visitors to Tumblr have grown by 40% since it acquired the blogging service in May 2013, and expects that growth to fuel more than $100m in advertising revenues in 2015.

Yahoo’s chief executive Marissa Mayer made the prediction in an earnings call with analysts, following the announcement of the company’s latest quarterly financial results.

“We acquired Tumblr a little more than 15 months ago. Over the past 15 months they have seen strong growth. Their audience grew 40% from 300 million to more than 420 million users,” said Mayer.

“The number of registered blogs nearly doubled from 105 million to 206 million, mobile monthly users of their mobile app grew by 50% and perhaps most impressively Tumblr time spend grew from 22 minutes to 28 minutes.”

There’s a caveat to this growth: Yahoo counts “users” as anyone who logs in to Tumblr to write a blog, but also anyone who visits one of those blogs. If you click on a link to an amusing single-issue Tumblr from another social network, for example, you’re being counted as a user.

In Yahoo’s eyes, this is Tumblr’s audience, and it hopes that will hold true for brands who might advertise on Tumblr too. Marissa told analysts that “more than 260 of the world’s top brands” are now on Tumblr, before talking up the impact of the company’s new sponsored posts advertising business.

“Tumblr’s revenue is growing nicely and we anticipate them achieving more than $100 million in revenue as well as positive EBITDA in 2015,” said Mayer.

This is still relatively small in the overall scheme of things for Yahoo: the company’s overall revenues for the last quarter were just under $1.1bn, as a comparison. But Tumblr’s importance to Yahoo is its potential to attract the younger internet users that brands are particularly keen to target.

Later in the call, Mayer was asked about adult content on Tumblr, and whether “NSFW” blogs will put advertisers off the platform. “I looked at a lot of different Internet services over the years. Almost all of them have some component that is not safe for work driven,” she said.

“I would say that Tumblr is not certainly not the highest I’ve seen... it’s how some people choose to express themselves and so its something that we support on the platform, but that is not as large a percentage as I’ve seen other competing services.”

Mayer also told analysts that Yahoo’s mobile audience is growing: up to 550m monthly active users across Yahoo and Tumblr. “We believe mobile monthly active users are approximately 17% from a year ago showing strong growth on an already large user base,” she said.

Yahoo is still in the market for buying other companies, although Mayer said that new “building block” acquisitions must fit with one of Yahoo’s four “pillars” of the company’s business: search, communications, digital magazines and video.

The latter is increasingly important for Yahoo, with rumours swirling that it wants to provide YouTube with some stiffer competition in the online video market – including poaching some of its stars.

Earlier this month, Business Insider claimed that Tumblr may be a key plank in this strategy, suggesting that Yahoo’s management thinks it “should become the company’s answer to YouTube” by signing up popular YouTubers to run their own channels on Tumblr.

Mayer gave no details on that during Yahoo’s earnings call, although she said video is an important part of the company’s plans, including selling video advertising.

“We need to make sure that we have enough streams from end-users, so we have enough people coming to watch video on Yahoo and our related properties on our network that we have places to place those video ads,” she said, before addressing the wider video market.

“This has been an area of a lot of consolidation this year and it’s a space that we are watching carefully, but it’s an area that we’re very bullish on.”

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