What To Do When a Competitor Steals Your Ideas

Nothing.

Keep doing what you are doing and focus on doing it better. Your ideas are stolen because they are good ideas - better ideas than your competitor can come up with on their own. 

Unless you have a patent on your idea, you have to accept that competitors are free to take your ideas. This sort of thing has been going on for an eternity. Indeed, you should be keeping an eye on what your competitors are doing as well.

What they cannot steal is your passion, experience, understanding or execution on the ideas. Keep focused and committed to delivering better value and expereince to your customers.