I am also an American. I grew up in the "Deep South" (the southern coast of Alabama), and my family and I never said "tell about" without a direct object. It was always "tell us about" or "tell me about." I think this may be more of a midwestern or northern American dialect, where German syntax has a lot more influence. I live in Milwaukee, now, one of the cities with a LOT of German construction, both physically and in the language. It's common to here someone say something like "I'm going to the store - do you want to come with?" - which sounds VERY German to me!