the 1st time this happened to me, the plumber said the wax seal under the toilet blew, he showed me how to remove the toilet (wet vac empty 1st) and replace the wax seal (bought in any hardware or walmarts) and replace the toilet. DH has since replaced it 2 more times in this house, and just installed the new toilet in our inherited house. The plumber was also able to ascertain the damage to the ceiling and wall (where the water followed the beam) and give me an estimate for homeowners insurance. call your plumber now.

Call a plumber to fix the water leak...but meanwhile drill ( with a non plug in drill!) a very small hole or 2 or 3 in the ceiling to allow the water to run out and not cause the whole ceiling to fall in.
Linda C