You should brush your teeth after every meal when ever possible. There are many brands of toothpaste with whiting that you can use that may help whiten your teeth. You should also avoid staining your teeth (ie with coffee soda and smoking to name a few) You should brush your teeth for two to three minutes.
I am not sure what you mean by brushing without stopping. I can only guess that you mean to brush for a longer period of time then the suggested two to three minutes. You do not want to brush to the point that you are hurting your teeth and gums. If your teeth are not getting white by brushing normally, then you may wish to speak to your dentist to get advise on what they may recommend you to do