Pew Research says teens are using Facebook less because of "watchful parents, too-old adults and drama - nasty conversations that would never arise in real life".
One research interviewee, 15, liked Tumblr because she didn't have to present a specific or false image and "I don't have to interact with people I don't necessarily want to talk to".
Social media expert Deirdre Breakenridge talked to teens who said Tumblr was less of a place to connect and was more an expression of themselves. One said: "Facebook has a connection purpose, but Tumblr is about me."
And it's getting bigger. Tumblr has 116 million blogs, covering topics on anything under the sun (and beyond the sun too). More than 90 million posts are made each day.
Findthebest.com says browsing through the various tumblelogs is like sifting through the lost and found department of the entire internet: "It's a beautiful mix of everything and anything, from the shocking to the spectacular."
There's plenty of "spectacular", with blog after blog showcasing wonderful beaches, cityscapes, sunsets, lagoons, clouds and more than a few supermodels.
There's also plenty of "shocking", so if you're starting a blog it wouldn't be a bad idea to tick the box blocking NSFW (not safe for work) content.
The internet has many dark recesses and, unfortunately, Tumblr makes those recesses a lot more accessible.
Yahoo!'s recent US$1.1 billion ($1.4 billion) purchase of the site may lead to changes, but the big challenge (besides making money from a demographic with none) will be retaining, in an ever-evolving social media landscape, the cool factor Tumblr inherited from the long-since-cool Facebook.