From schizophrenia.com
About 52.303 million people worldwide suffer from schizophrenia.

From nytimes.com
Auditory hallucinations are a hallmark of schizophrenia: 50 percent to 75 percent of the 2.8 million Americans who suffer from the illness hear voices that are not there. A small minority of the patients said the voices they heard were always or almost always supportive and positive in tone. But more than 70 percent described them as always or almost always negative.

So, about 22.75 million people hear negative voices.

From http://www.schizophrenia.com/suicide.html
Between 10% and 15% of people with schizophrenia have historically committed suicide.

From http://en.wikipedia.org/wiki/Schizophrenia
About 5% of people with schizophrenia commit suicide.

Taking a simple median, about 10% of the people who hear negative voices will commit suicide. That's about 2.2 million of the people who hear negative voices at this time. Many of those will suicide due to endless degradation, insults, and mental rape, where they have no one to help them.

There are no statistics that describe the percentage of people who hear negative voices who are being attacked from an external source, however:
In all of the accounts I've analyzed, people are describing voices that are being created by something that can think. All of the accounts appear to describe the origin of the voice as a being or person that can both see the victims thoughts, and speak to the victim, without the victim being able to perceive the attackers logical planning thoughts. It would be difficult for a reasoning piece of one's mind to spy and cast it's voice in this manner. Also, the victim would remember the piece of mind training to spy and cast it's voice. The negative voices appear to operate by a common pattern of behavior, e.g. endless insults, sexual stimulation, etc. These facts are arguments for the attackers being from a source external to the victims mind.

Given these arguments, the vast majority of the approximately 22.75 million people who hear negative voices may be misdiagnosed. The total number of people being attacked may be larger yet, given the number of people who believe they are targeted individuals and people who believe they are demon possessed. About 4% of schizophrenia cases are children under the age of 15. Approximately 890 of those diagnosed with schizophrenia who hear negative, insulting, degrading voices, will commit suicide today.