There is no way to acknowledge a "Like" you have received. I don't think anyone expects an acknowledgment when they "Like" a post in the same way there is no acknowledgment when you "Like" a post on Facebook or "Favourite" a tweet on Twitter. If you wanted, you could start a conversation with the person. This thread explains how. You may also find this useful.
Hi, JacquiM. I nearly missed this post, there are so many newbies to greet this morning. I didn't mean to confuse you. You get "points" and cheery little messages for giving and receiving "likes." Many times I don't have anything to contribute to a thread, but the conversations are educational and/or entertaining - those get "likes."
Anyway, it's time for me to start my day. Last minute Granny duty in a few minutes.