I'd imagine the forum gets a lot of threads about vibrato, but I hope you all don't mind another.

How do you guys do it? Whenever I try it's too slow, and when I try going faster then the sound isn't noticeable...

make sure everything is moving right, wrist and finger. and that your fingertip is moving as far as it should. its really hard to explain in words. your wrist doesn't actually move, your hand moves on top of it. (put your arm on your chest and move your fisted hand back and forward like knocking without moving your wrist.) and if you put your finger on your thumb and push it and your thumb forward that is how your fingers move. the difficult part is putting it together. personally my vibrato is questionable and i;ve been working on it for a year and really hard for a month. just keep working at it! it will come in time, some people just get it straight away!
if have a teacher then make sure that they help you, ask to spend a certain amount of time each lesson to learn it. if you don't have a teacher get one! they are invaluable!