It's not really standard in English to use terms of address like this. Really, outside of very specific situations (courtrooms, as an example), it's pretty rare to use a term of address and when we do, it's always related to their job. Examples include:
- "your honor" for judges
- "officer" for police
- "professor" for professors
- "captain" for ship captains and people of that rank in the military (all military members can be addressed by their rank)
- "doctor" for doctors
- "sir"/"ma'am" - often used by children when addressing adults or by adults to refer to anyone above them socially.
"Master", specifically, is problematic. You run into the issue of the slave/master connection which either hearkens back to the US Deep South's past... or the more modern usage within the dom/sub community. Neither of these inferences are something you want to risk.
If you want to thank someone on the web for something, there's really no need to add a term of address... if you absolutely need to, say "doctor", if that's what he is, or "sir" or "ma'am", if you know their gender for certain... but I (personally) find it annoying when people add terms of address on the web. We're in an informal world here... I often have people call me "sir" and it's a pet peeve... firstly because I'm female, so it's presumptuous to assume everyone on the internet is male and secondly... it's just not necessary and doesn't mean anything to me.