Hello, how are you? I hope you're fine. If you want to make more formal greeting or address, you may use such turns as:
1. "Дорогой ..." - "Dear ... " - very informal
2. " Привет дружище, как поживаешь? " - Hi buddy, how are you doing? - informal
3. "Уважаемый .." - You use this if you want to be very formal and you want to show your respect to that person.