Hearing voices or auditory hallucinations, are symptoms of what is known as a mental state called 'Psychosis'.
Schizophrenia is one of several psychotic disorders. If you, or your friends are hearing voices, seeing things which are not real, feeling things that are not real or smelling things that aren't real, it is very important you consult your doctor as soon as you can.
Psychosis, is a serious medical condition that needs appropriate professional help. If you had a lump, getting larger on your chest, would you see a doctor? Most likely. Treat mental health in the same light, psychosis is serious, and it's very important you get help and you'll be on track for recovery in no time.