I reply to all my messages, either with information, or if I have nothing to add then I let them know also. My son had a DNA test for Christmas 2017 from his GF, and has no interest. I have just worked out how to get management of this so it can be part of my tree.
He has had one message - he gave me the log in - I did reply, weirdly they never responded. so guess it works both ways!
It might depend what you are asking? Someone messaged me years back on Genes Reunited and got quite rude to me as some of my tree was private, I responded, but never bothered when he was so rude. Have you tried a surname search on here? you never know someone may be linked and on here.