This idea of increased mass is very misleading. If you get on a ship and accelerate to 99.5% of the speed of light, nothing on the ship changes in any way. However if a particle of mass m is moving toward you with this velocity its total energy is 10 mc^2, which is the rest mass energy mc^2 plus a kinetic energy of 9 mc^2. There is a similar increase in momentum to 10mv. Some people like to call this kinetic energy and momentum increased or relativistic mass. This would mean that it is the mass that increases from m to M = 10 m and then momentum would be given by the usual formula Mv and instead of kinetic energy we have increased mass energy given by Mc^2.
I think this is a little absurd and apparently the opinion of many of educators in relativity has been shifting in this direction. See my thread entitled "Idea of increased mass at relativistic speeds" lower in the list of threads, for more details.