[webdisrupt]

Quite frankly you should see this as an opportunity to start your own thing. More importantly I would question why weren't you promoted especially being the one of the first employees? Assuming you have done nothing to piss the founder off, you should be truly appreciated for what you have achieved whilst motivated through career progression etc.

Also bare in mind that this is a normal process for SOME companies as the more they grow the more people are hired so as to try and achieve more (this is debatable) work thus higher revenues.

Personally, I would see what you really want from life and if you are seeking credit/appreciation for your own work then

start a new business or co-found a product or join a startup that is prepared to give out equity