Leona Lewis, Girls Aloud and Arsenal boss Arsene Wenger have posted personal anti-bullying messages on the internet.
They're appearing on the first online anti-bullying channel, which has been launched by the Beatbullying charity and video sharing website, YouTube.
The channel has been created to help the growing number of kids who say they are being bullied through the internet.
It's hoped it will encourage others to upload their own anti-bullying videos to help stamp out cyber-bullying.
In their message, Girls Aloud say you shouldn't do anything you wouldn't want done to yourself.
"If someone's being bullied and you record it on your mobile and put it online you're just as bad as the bully and you will be caught," they say.
Sarah Dyer from the Beatbullying charity said it was too easy for someone who would never consider being a bully in real life, to do something online that they thought was funny, but was in fact bullying.
Her message was backed up by other stars who've posted messages, including X Factor judge Dannii Minogue, Strictly Come dancing contestant Penny Lancaster and Boyzone singer Ronan Keating.
Ronan says: "If you wouldn't say it to someone's face, then don't post it online."