Does it still work or are they still broken?
No, it does not. It's a read-only function. Along with TimeLength and TimePosition for sounds. They may work studio, but will not in roblox player.
IsPlaying() does work in the player despite obscure's comment. I have already tested and use the method my self. It's never meant to be a writeable property; it's always and should always be a read-only property. Granted sounds are slightly neglected with events, to answer your question, it does work.
TimeLength also works online.