Almost all of our beautiful heirloom tomato plants were eaten in one night. The central stems were eaten and the plants are now just sitting there not growing. It was deer. We have sprayed them now-(see the thread about deer eating tomatoes). But it is too late-kinda like shutting the barn door after the animals have gotten out. Make yourself some home made deer deterrant spray, and maybe consider replanting them if they are really eaten.

If the stalks themselves are gone, it's deer.

If the bare stalks are still there (except perhaps the last few inches of the growing tip), but the leaves are missing, and only the stems that support the leaves remain (technically not stems or branches but petioles -- each petiole supports a single compound leaf), you probably have hornworms. They will eat blossoms and fruit as well.

Hornworms have some of the best camouflage in the world: you can look right at them but not see them. They are active 24 hours a day. They leave distinctive droppings shaped like 1/4" dark-green blackberries. The droppings can be found under the damaged area (on leaves or on the ground).
hornworms and their damage

I heard in India its the water buffalo

It's gotta be deer then....I didn't think they ate Tomato plants. At least the whole plants haven't been eaten....probably still salvageable if I get some type of deterrent down.

Yeah, that's deer. Notice the edge that they bite off is never a very clean cut, because deer have only one set of front teeth and press them against an upper jaw pad to tear off foliage. They always seem to be too lazy to eat the entire plant and prefer to nibble out the tops instead.

Around my area deer eat the tops of big plants, and eat small plants (tomatoes) down to a 2" stem stub. The problem has gotten worse the last few years in our suburbs. You can see a deer standing in someones front yard eating off a tree in daylight.

I put out dog dishes with water outside in case a animal wants to eat a tomato for the water content.