You could say "Hola, esta es su amiga hacking su página Facebook." Many computer terms go directly to Spanish from English, especially slang terms like "hacking".
Facebook es aburrido
inscribete con Facebook
Estoy en facebook.
Agregame en Facebook
Buenos Dias Facebook
Tienes un accuenta en Facebook?
To say hello friend in Spanish you can say "hola amigo".
You could say "¿Por qué estás en facebook?"
bueno no mis amigos del facebook
Estas conectado(for guys), conectada(for girls) en facebook?
If they say 'Inbox me!' or something like that they mean they want you to add them as a friend on facebook.
my friend = mi amigo