How to reply to replies.

Ermm, so, I have a question, let’s say, I create a thread, and a bunch of people reply, and I then want to say ‘thank you’ or something……if I send a reply using the ‘reply’ button, then the people who replied, won’t be notified of my reply and won’t see my reply unless they go back to that thread.  I could send each person a direct message I guess.  Any better ideas?