I don't know how to search for it, but if you have an approximate idea, just start typing a message. When you have a few words, type @ then a list of options comes up. The more letters you type after the ampersand sign, the more accurate your choice will be. So I can type a message to @busso and use a drop down menu to fill in the rest with just the letter "b" after the ampersand.
Private messaging is a different thing, but the "@ name" will make sure that the intended person sees your public message.
Hope that helps.