Suicide is not murder unless you understand "murder" to mean "to kill a person". But we don't so understand it, as we don't usually speak of the hangman's murdering the convict, or of a soldier's murdering his enemy, or of someone's murdering in self-defense a man who was trying to kill him. The point is that murder involves a killing one had no authority to commit. To claim that suicide is murder, one would have to argue that I have no authority to take my own life. But why not? For a fascinating defense of the claim that I do have such authority, read David Hume's essay "Of Suicide". As for the claim that suicide is wrong because it makes something of value disappear from the world, consider (1) whether I do not sometimes have the right to destroy things of value and (2) whether events can sometimes so conspire against us that our lives simply don't have value and there is no reasonable prospect for a change in that regard.
Suppose someone is thinking about killing himself. Can philosophers or philosophy give him reasons for or against doing it? Or isn't suicide a philosophical subject?