If that doesn't work usually it's best to address someone with a question.
For example, to ask someone a question you may want to use this format to do it and to talk to others the same way: Person's name: Your question Most of the time you will get someone's attention this way.
For a much bigger list the WBS Chat Book has a whole list compiled from various users from all over including various smileys!! If you choose you can use text editing to increase the size of your text to catch someone's attention.
Try not to yell, this is where you either type in all capitals or use text editing to increase the font size and bold type of your message.
In IRC's you can only type in all capitals, there is no text editing.