Just Google “netiquette”.
It doesn’t seem to say anything (although I just skimmed it) about responding. Points of interest are not correcting others’ spelling errors, not using ALL CAPS, not multiposting, and staying on topic (I think I’m guilty of some of these).
Even if it’s not on WP, it’s still common decency to say “thanks” when given solicited advice, and possibly when complimented (although there’s the mitigating “blush factor”).