How can I get a message to someone if they aren't following me?

Ok. I follow a few celebrities and sometimes they will make a good comment and I want to reply back. So, if I'm following them but they AREN'T following me, can they still receive the tweet and possibly answer back, if they desire? Because I had my friend stop following me so I could send him a reply to see if he got it, even though he wasn't following me anymore. He told me no. So I just want to know if I'm wasting my time writing these replies and they aren't even getting them or is there a better way to message them even though they don't follow me. I mean, a celebrity isn't going to follow everyone that tweets them, but they should be able to at least respond to one message, or reply.