Thessaloniki used to be called "the city that never sleeps", just like NYC. Even though this is not totally true anymore, you can always find another place to go for another beer, in case you really wanna stay out till the morning.
The city's nightlife has been changing a lot, during the last 10 years, but it has always been very versatile. You can do pretty much anything you'd possibly like. From trendy cocktail bars to old-school rock bars and from bar with live music to bouzoukia (venues with live greek music, usually way over-priced), you can still find a place to satisfy your needs and desires as a guest.