One of the reports on the Mission Control screen is the Areas you are losing $ that need monitoring report. This report was designed to show you which specific Ad are losing you money. It's great to know where you're making money, but it's also important to know where you are losing money also. Certainly most ads will take time to make money, so you'll want to keep an eye on the ones where you're losing so you can make decisions on how to proceed with them.
Below is a video to show you exactly how this report works.