i cant vind him
Blue can be found at the Cinnebar Islands near the Pokemon Center. You can only Battle him in the Viridian City Gym once you obtain all 15 Badges.
If this is HeartGold/SoulSilver, then the 16th gym leader is Blue. He's in his gym in Viridian City. However, you have to talk to him on Cinnabar Island first.