Similar story from me. My daughter spilled apple juice in my wife's 2012 15" MacBook Pro. I actually dismantled the entire keyboard and cleaned between the membrane layers to clear the shorting from the printed circuits. Unfortunately, when separating the membrane layers, I was not cognizant of the Caps Lock key's LED attached to the membranes and damaged a couple of traces. Now, this Mac won't power on either and I am awaiting a trace repair pen so I can fix it.
The trick for now? Perform the power reset that you can find in many internet sources: Disconnect the battery and magsafe power connector. Press the power button for 10 seconds, then while still holding the power button, connect the magsafe connector to your MacBook. Hold the power button for another 10 seconds. At this point, try to start your Mac normally (this never works for me). Next, reconnect the battery connector. This should power on your MacBook Pro. It works for me. Of course, this assumes your battery has a charge :-) You will need to reset your system clock after this procedure.
You probably don't have to go through the whole power button procedure because it is assumed that the power circuit in the keyboard membranes is shorted out, but using just the battery connector method does not always work for me, and the full procedure always does. NOTE that you CAN use an external keyboard still if you can get your keyboard powered on. I suggest disconnecting your keyboard ribbon cable from the logic board to avoid further damage to your Mac.
In the interest of keeping my last answer to novel length Vs. epic length, I did not mention that unless an entire pitcher of water was spilled on your MacBook, the logic board is probably fine. The keyboard has a rubber overlay under the keys. The overlay does have holes in it for mounting the keys. However, between the keyboard and the logic board is also a solid layer of thick plastic AND the LED medium (a thin layer of plasticy paper) that is glued to the frame around the edges. So....there are many layers of protection between your keys and the logic board. Good luck!