I don't think so. You reply to people just like this. It shows the responses in the bottom left, you click there, and can reply

you can "private plurk" by moving your mouse over your friend's name, a box with an arrow appears, click on it, & click "Send private plurk"

yes you can MichelleM just like i just did, you just dont see the @ only the name linked

thanks for telling me bout this dude!