This is so sad. A very close friend of mine went through something similar.
Her daughter who I believe was 14 or 15 at the time met a girl on-line who lived not far from them, maybe 35 minutes. The girl she met (Tammy) was depressed, and bi-poler, she was also adopted and the parents who have struggled with this girl from day one. She has many, many problems.
These girls started to write to each other and whenever Tammy got depressed she would get nasty, angry toward my friends daughter. At the same time she tried to have a lesbian relationship with this girl. It was so strange and I don't have all the facts but in the end the girls decided to make a suicide pack. Tammy totally brainwashed this poor girl who yes did suffer from depression. Luckly my friend got fed up with Tammy calling 10 times a day and called the parents home. She spoke with the dad and he then informed her of this pack they had made. The two parents worked together somewhat and managed to serperate the girls. I know my friend suffered horribly as did her daughter. To learn that your child wants to kill herself................... Well it brought my friend to her knees in tears. Anyway my friends daughter went into therapy and is on meds she is leading a happy and normal life. What ever happened to Tammy is any ones's guess.
Parents really need to be involved in their children's lives. Know who their friends are especially on-line friends and yes I know what I am saying is most difficult, children hide things, parents work all hours. But in these cases it is a matter of life and death.