This may or may not be the case.
If so, please correct me.
A question that keeps coming up is: why don't they go to the police?
So a terrible event has happened to an individual.
Now they can go to the police where they will be bombarded with lots of questions.
This will be followed by a really long court case where they are treated as a liar by a very obnoxious defence lawyer.
Then there is the possibility that after this very traumatic process, the criminal won't receive justice.
Though the court of social media, a prosecution is guaranteed. Granted it won't lead to any time in prison but it has some benefits.
The accused will have their entire life ruined. They will be unemployable, their marriage might end (if they're married) and the social services will immediately take their children away.
Further more the accused will be harassed repeatedly. Even friends and family of the accused will get a battering from on line media. The person will become toxic waste, and no one will want to befriend due to fear of ostracisation.
So social media provides one form of punishment to the accused. Sure the accused may continue to commit said crime (if they are actually guilty that is), but at least they had some comeuppance.
So yes, I can see the appeal of going to Twitter and Tumblr instead of going to the police.