How to reply to a message via REST API?

On the Message object, there is a reply method (for example /restapi/vc/messages/id/245/reply ) that will allow you to post a reply to the given message.  It works much the same way as posting a message to a board.

Go check out the KB article about this topic

http://lithosphere.lithium.com/t5/Growing-Successful-Communities/Replying-to-a-post-via-REST-API/ta-p/8569