In emergency dial 110. Having said that, the Berlin police have a useful website here. It even has some stuff in English and you can phone them in non-emergencies on +49 (0)30 4664 4664 and some of them speak English. If you need to report a crime, say for an insurance claim, they have a form in German that you can fill in here. For the English crib sheet click (or right click) here. The crime report form has strict warnings against making false reports.
They aren't interested if you have just lost something. For that try Berlin lost and found at Templehof airport +49 (0) 30 90277 3101 or the BVG (trains / buses) lost and found office at Potsdamer Strasse 180/182, 10783 Berlin-Schöneberg. That's also where you pay fines when you didn't have a valid ticket. Phone +49(0)30 19449.