could this be a thesis for this topic When Bullying Turns Deadly: Can It Be Stopped
Thesis" Bullying causes many problems in teenager's lives such as stress, depression and suicide
That's not a thesis statement. It's just telling what everyone already knows.
http://leo.stcloudstate.edu/acadwrite/thesistatement.html
Read through and study the before-and-after examples here to get a clear idea, and then revise.