What I can share here is that God has convicted me of this and he has given me the grace to overcome it. I am not perfect but God has shown me, as bob mentioned, that this is an issue of self-control, and He has further shown me that the urge to touch is rooted in the lust of the flesh. The reason I know this is because if my eyes are not straying where they should not, and I keep my mind on pure things, I don't have any desire to do it. When I am not practicing self-control, I can see the lust filling up like a tank within my soul, and Satan knows exactly where the fill-line is. When I drink those things in I am giving Satan the fuel to overcome my self-control; it is basically like giving a thief the code to your home security system. I will note that I think that unless you have completely submitted the issue of relationships to the Lord you will have issues here.
I see some people say it's natural, it's a stress reliever etc. Well, the things we naturally want and do aren't always right. The flesh itself is corrupt and the mind is more than willing to agree with it if we do not exercise self-control. I believe masturbation is a stronghold for most men and no allowance for it should be made. Despite what some people are saying here, God will give you the grace to overcome it if you are willing to submit and surrender it to him. I think many men use it as a release valve for their troubles when we are supposed to cast all of our cares and anxieties on Christ. Basically, it's a poor substitute for the peace we can only get through Him.
I would just encourage anyone who makes a practice of masturbation to examine how you are using it to substitute for what only Christ can give to us, which is peace from all of the worries and cares this life brings. If you are using it to feel better, know that what you really need is His joy. If you are using it because you are lonely and desire intimacy, know that you are not alone and what you really need is intimacy with God. In every respect, whatever comfort it is bringing you, what you really need is Christ and not to appease the desires that are driving you to do it. When you start looking at this you will see that these two things are actually diametrically opposed to one another.