Why would a person announce on a social network they are going to kill themselves?  Because they want to see if anyone actually cares.  It is the last attempt at asking for help.  Most people tend to isolate themselves from people that get sad.  Instead of getting the positive feelings which conversation and human contact can create that sad person gets emptiness and loneliness.  Some resort to cutting themselves because they can't ask for help.  Even then most times it is ignored.  Eventually everyone you care about will push you away cause you are not perfect.  Because you struggle more than most to handle the intensity of emotion.  Soon you stop trying to interact with people in person because you need to much.  The voices of the past never leave you.  School doesn't make you stronger, it rips you apart. 

You go online, interact with other digital people.  You can even live a virtual life where you can have virtual sex cause that is fun.  Soon you have no real human contacts.  One day you wake up and it hits you that you have no real friends.  You panic cause you need someone to care about you.  Things cascade, for some reason the darkness comes, you make one last ditch effort as the emotion grabs you and you swallow too many pills.  Nobody comes and your life ends. 

A single act of random in person kindness could of saved..