I have a 6 year old moen vanity faucet, the hot water handle rotates without stopping, but I can turn the water on and off, what is the problem?

Tour stop tube's missing(see image) Call Moen and they'll send you one free of charge.
.Call: 1-800-BUY-MOEN (1-800-289-6636)
8:00 am to 8:00 pm Monday through Friday
8:00 am to 6:30 pm on Saturdays EST
Closed on Sundays and all nationally observed holidays.
To contact Moen Canada call: 905-829-3400
Good luck, Tom

Tom put up a pic of the stop for a single handle fuacet, but Im thinking you have a two handle? If so, take the handle off the hot side (the one that spins) and compare it to the cold handle. I bet the handle itself is broken on the inside. If this is the case, you just need a new handle. It may also be the cartridge has broken, in which case you will need a new cartridge. Inspect the handle and cartridge and compare to the cold side to see what's broken. Then, as Tom suggested, call moen for replacement parts. Not sure if they will waranty the handle, but it should be a fairly inexpensive part. Let us know what you find. Good luck.