Facebook Chat Not Working Properly For iPhone 4

I recently bought the iPhone for, and am having a pretty annoying problem with the Facebook App.

So, in my Facebook, I have a group for my friends (one group). Now, when I'm on chat for my iPhone, I can not see ANY of those friends in the group online.

I read around a bit, and was advised to try unticking the group, so all my friends were shown in one list.

Did that, but still no luck..can't see people from that original group online.

Any advice?

Thanks in advance!