Are you sure your doing it right? Only you and the person you are whispering to should be able to see it.
Below are instructions on how to whisper in pogo chat.
Whispering in the chat rooms is very easy. Basically, it's a way for you to send chat to one specific person in the room. Only they can see your whisper, so it's a good way to communicate with just one person when you don't necessarily want others listening in on your conversation.
To whisper, type /whisper followed by the screenname, into the chat room. Like this:
/whisper pogorules I just whispered on Pogo!
Pogorules would then see:
pogorocks<whisper>: I just whispered on Pogo!
You can only whisper to one person at a time, and no one else can see your whispers. If you have any other questions regarding whispering, please let us know!
They also have private chat now in Club Pogo. Not sure if they have it in free accounts.