I just got the Throw Voice shout, but whenever I try to use it, the shout goes on cooldown, the caption comes up, but there is no voice and no one reacts to it. What could the problem be?

You use it against walls. And only alarmed NPCs react to it (meaning they must be already searching for you.)

ive had no problems with this shout, its very helpful when being a sneaking character.

as opposed to sir glitchalot's reply, ive used it against people who arent looking for me as well.

all i can say is make sure ur not hitting the person with the shout and make sure your not casting it too far into the distance

I think what Sir Glitchalot was trying to say is that the person has to be hostile towards you. Which makes it useful in dungeons. It won't work unless you see a red dot on you compass meaning that they are hostile. So it won't work on villagers or town guards.

He is saying they need to be actively searching for you in order for it to work. This is false, as long as the person is hostile to you the shout will work on them (whether the npc is searching or you are completely hidden). As others have said, don't aim it too far away and aim it at either the ground or walls.

It's pretty much the same as if you shot an arrow over their heads -- they react to that sound too.

It needs to work on town guards. The mix of "Wizard's Guards" and "Town Guards" in the Dwarven Museum made it a true lesson in frustration using that shout during the Thieves Guild quest line.

The wizard guards would run after it and at the same time the town guards would come over and tell my stealthed character to stop using my shout.