I logged into iCloud.com but there is no option to send an iMessage.
Is it possible to send an iMessage through iCloud or any other website?
For the moment Apple has been extremely quiet about how to access the protocol, and there has been no confirmed plans for iMessage to for the Mac. However, they will most likely release a version for every Apple platform.
I don't think however, they will create a web interface, since no one else has really come up with one that works well.
Aha! Look this website: http://www.imessageweb.com, it can send an imessage through webpage!