Rake
is the name of a utility - see more info here - so you can't just call the utility. It's like opening your web browser and expecting it to do something for you by itself with no instructions.
Try running one of these:
heroku run rake db:create
heroku run rake db:schema:load
git push heroku master
< make sure you've pushed whatever you want to show up on heroku to your github before running this command.