I have decided to put a hitch on my vehicle and get a new bike carrier. I am looking for the platform kind, not the hanging. Do any of those come with locks? I know some roof rack ones do, but Im not having any luck finding hitch ones that do.

I use a Yakima stickup platform hitch rack and keep a cable lock on the center mast - lock my bike to that or the trailer hitch when away from the car.

I do the same, loop the cable through the frames, then lock it to the hitch.

Kuat NV and 1UPUSA have available locks

No matter what lock you use I wouldn't trust it to leave my bike unattended for any real amount of time.

Most rack locks are just a cable. The one on mine is more convenient being built into the rack, but it's not any better at locking or anything - it's just a cable.

I've heard of some of the wheel mount racks having a lock on the part that grabs the wheel - I don't know which ones offhand though. It would be a little more secure than a cable but those rack arms are not difficult to cut through either.

The only type of lock I would trust to leave my bike on my car while out of sight (like in a restaurant where I could not see the bikes) would be a chain connected to the hitch (or the rack if it's solid enough). Other thing I've seen is putting the bikes inside the car with tinted windows - someone could still break into the car, but if you only park your car in non-sketchy areas it's a lot less likely.

I have used a Kryptonite New York Noose 1213 before that way to secure my bike to my car:
New York Noose 1213

Drawback is you don't want to drive around with it that way. But I figured it's about as safe (when connected to the metal hitch) as my cheap uhaul I use elsewhere. That's what I use for my more moderately priced bikes, I wouldn't leave my expensive high end full carbon bike locked up outside anywhere really.

I have the four bike version of this rack and it's great. It has built in locks in the ratchet hooks. I don't like the cable system like others have mentioned because anyone can cut it and take the bikes. I really like this rack and the price is not bad. It's well made and holds the bikes in place with no movement whatsoever.

TransIt Flatbed 2DLX 2-Bike Hitch Rack