I'm a very new member. I've done a search and this topic doesn't seem to have been covered except in the occasional passing reference. Apologies if it has and I have missed it.
KEEP YOUR KIDS AWAY FROM TUMBLR!
This is a blogging website. That means that a member (such as my DD) can very easily set up her own blog. Nothing wrong with that you might think. They can post funny messages, charming pictures, gifs, exchange views on their favorite TV progs. My DD is a frequent Tumblr user. It was only when she started to have various problems that I took an interest in what can be found on Tumblr. For starters, plenty of porn. But I only mention that in passing because that part of it hasn't impacted us. Many kids with depression, self-harm issues and eating disorders set up blogs on TUMBLR. Some believe this is a form of therapy - and maybe for some of them it is. Some of the blogs promote anorexia as being a life-style ("pro-ana") others chronicle their experience of it. The point of TUMBLR seems to be to feel popular, by getting other members to "follow" you, by making your blog as interesting as possible, by re-posting interesting content. So where you end up is with dozens of blogs posting images of emaciated girls and/or self-harm, all following each other and re-posting the same content. It seems to me that the blogging is an addiction as much as the underlying illness (though in itself a less harmful one) and as far as I can see, spending all one's free time doing this is not therapeutic at all, it's only going to wind them up even more.
I've contacted TUMBLR myself over this and they're not very helpful - they say they have "recently become aware of the issue" and will start to remove such content "when the time is right" - I take this to meant they are not going to take any notice until a few of their members have starved themselves or bled to death after continually provoking each other with these images and messages. Online giants like Facebook are going to bend over backwards to avoid being criticised for this sort of thing. But a smaller company like TUMBLR, keen to increase its user-base, has no such qualms.
My advice is (a) BAN TUMBLR and other blog sites until they can guarantee child-friendly content. (b) If you can't and your DD is a member, insist on knowing their blog name and viewing it regularly - make sure they do not have a secret one. (c) Find a way to restrict usage to a reasonable period of time each day - this can usually be done very easily through your wireless router. (d) switch off your router at night. (e) Go to the Opendns site and read how you can very easily monitor and filter all of your household internet traffic, free of charge.
Spread the word. TUMBLR is not a safe site for our children.