Butter melt inside the toaster
By toaster I am assuming you mean the type that has slots that you pop the bread into from the top.  Normally they also have a removable tray at the bottom, which you say you have taken out and cleaned.  Shaking does normally work, but this can also lead to breakage...  so maybe not quite so vigorously would be a good idea.  I don't understand why you have butter inside your toaster, but that is irrelevant now - so how to clean it.  I would suggest opening some windows, and getting the toaster as close to an open window as possible, and putting it on repeatedly until it stops smoking, you are basically just burning off what is left in the machine.  Just as a side note, every time you use your toaster, after it has cooled down, turn it upside down and give it a little shake, and try not to put anything other than bread in it.  If you want to make toasted sandwiches or anything with butter/cheese, get a toasted sandwich maker.