No, I've never seen the devil -- and I hope I never do, because the Bible clearly teaches that he is the essence of absolutely everything that is evil, including death itself. Jesus called him "a murderer from the beginning, not holding to the truth, for there is no truth in him" (John 8:44).
But I certainly have seen his work -- and so have you (even if you didn't recognize it as such). When someone commits a crime or hurts someone, Satan rejoices. When someone yields to temptation and ends up destroying their life, Satan rejoices. When wars break out or families can't get along, Satan rejoices.
Remember: The devil's goal isn't just to do bad things occasionally. His goal is to block God's plans in every way he possibly can, and one way he does this is by trying to stop everything good that God wants to do. Don't be deceived; the devil hates us, and all his promises are lies. One of Satan's cleverest schemes is to deceive us into thinking he doesn't exist. But he does, and the evidence is all around us.
Yes, Satan is real, and he is our enemy. But listen: he also is a defeated foe! By His death and resurrection, Jesus Christ conquered sin and death and Hell and Satan, and someday His victory will be complete. On whose side are you? Don't be on the losing side, but by faith commit your life to Jesus Christ and become part of His eternal family -- beginning today.