Spaniard here; addressing someone by the last name looks really outdated.
<First name>: Informal, casual conversation.
Don <First name>: More formal, conveys respect while still indicating some closeness.
Señor <Last name>: Most formal, normally used in writing.
Using only someone's last name is just plain weird. If you want to speak formally to someone just address them as "usted", it will get you the same goodwill without sounding off.
And even with that, people under 35 will just stay at the informal (normal you) "tu" case.
The only situation where I call people by their last name in my language is when it's their nickname. Like there were two "Johns" so we call the second one "Smith".