A lot of views and no replies ... let me help!
You kind of answered your own question. Autotune is a huge factor - so you definitely need pitch correction (antares,melodyne, whatever).
You also have to sing faster... what they call rap/sing. You're rapping but in a melody hitting actual pitches.
For the intro of the song it sounds like there is harmonies underneath the main pitch. This could have been with a harmonize effect or he could of actually sung a different melody down lower.
When you record, try to imitate his style in the raw recording as well.
As for the weeknd, he sings falsetto all the time with a lot of reverb, echo, and ambient adlibs. Lots of harmonies too and melody variations.
Best of luck! I'm a big fan of both. Rep 6IX!
-Yovi