Most regulars on AB look back at the questions they've answered. We do this to see if there's any response (such as a 'follow-on' question) from the questioner. So, if you want someone to see your acknowledgement of their reply, simply post an answer to your own question.
The site isn't really intended to be used for 'chat' but some 'conversations' occasionally take place this way. If you particularly want to someone to correspond with you, it's best to post your e-mail address. (I sometimes do this. I normally create a separate address for each person I invite to contact me. If that address gets flooded with spam - which hasn't happened yet - my main Inbox still remains spam-free).
Chris