On Monday afternoon, this video was posted to a thread on /b/ with the words, "Find this dumb little bitch and throw her into a river."
This is a much worse situation than the lady tossing the cat in the garbage can for a couple of reasons. The abuse in question is a girl throwing very young puppies one by one into a river where they presumably die. It could be argued that they don't suffer much and it's no different from euthanasia, though. I don't know. I'm no expert on puppy drowning.
But the other reason this is worse? Nobody has come forward. Nobody confessed. There's no hard evidence of who did this and that hasn't stopped a group of /b/tards from tracking down the people they think are involved on Facebook and harassing them and their friends and family members.
Here's a screencap of the 4chan thread where it's all being discussed and the Gawker article I found it from.
The clever thing about /b/tards turning to Internet vigilantism is that they can get a lot more people worked up. Moral outrage is a fantastic tool for getting people to do questionable things, such as harassing some random girl on Facebook who may have no idea what's going on at all.
Never fear, though. A number of them have no interest in being "justicefags."