The former catwalk beauty admits she was a ""mean girl"" when she was just nine, but she soon learned how nasty and hurtful people's comments could be when she was subjected to the vicious taunts two years later.
Now Banks is urging her devotees to fight back and support the Stop Bullying: Speak Up campaign, which encourages troubled youths not to suffer in silence.
In a post on her Facebook.com page, she writes, ""Being kind is the fiercest move you can make! Take the pledge to Stop Bullying: Speak Up.""
And, in a video message to fans, Banks says, ""Join me to help stop bullying by speaking up. Now take it from me, I have been on both sides of the fence. At nine years old, I was a bully. I was the mean girl: 'Oh you can't hang out with us' - I was that kinda girl who used to say that kind of stuff.
""Then, at 11 years old, I lost a lot of weight and grew a lot of inches in only three months and I became the one that was bullied - the victim. So I got to feel the type of pain that I was inflicting on other girls when I was younger.
""Bullying is not right, it's not good. It's serious business and nobody should feel the pain of bullying.""
Banks isn't the only star wanting to stamp out the cruel behaviour - Lady Gaga has also taken a stand and wants U.S. lawmakers to make bullying a crime.