Do layers make hair thicker?

My hair is cut "like" Justin Bieber's (even though my hair was cut like this before he had it, ugh) anyways, my hair is pretty thick with some layers. I wanna thin it out, make it more fine. My hair is at its thickest after it dries, which I hate it. So, what I'am asking is, should I get more layers or will it just make it thicker? Also what type of shampoo and conditioner should I use? Be aware that my hair gets oily fast and has some dandruff. Please help me!