Criticizing His Life
Justin Bieber
I highly doubt Bieber or anyone else is going to make someone famous by going after them on Twitter. It could get the individual more "followers" on Twitter, but fame, highly unlikely. Sometimes mainstream celebrities take comments way more seriously than the person issuing them. A part of being famous means people will write and talk about you. At the end of the day it's free speech and free press (provided it's not defamation or a threat).
Bieber also briefly addressed claims he is having a meltdown by stating, "I'm very much in control." However, many people, including some of his fans, are concerned about him regarding the legal and social trouble in his life, keeping his name in the headlines via controversy.