Turns out the reason we might not find a lot of US citizens in the Panama Papers is, they can hide fortunes so much easier at home. Governing Magazine, emphasis added:

Earlier this month, 11.5 million confidential documents were leaked from a Panamanian law firm, exposing how some of the world's richest people hide assets in shell companies to avoid paying taxes. It’s the largest leak in history, and among the so-called Panama Papers' many revelations was that the seventh most popular place to set up shell corporations was in Nevada.

More than 1,000 companies have used Nevada to hide their money. Delaware, South Dakota and Wyoming also emerged as popular places to stash cash.

...Meanwhile, Delaware’s most recent financial report touted another record year for the number of new entities registered in the state. Delaware’s 1.1 million registered corporations outnumber the people who actually live there.

The Panama Papers have raised concerns among many here who say it's hypocritical of the U.S. to complain about its citizens hiding assets from taxation in offshore accounts when some states provide the same service for foreigners. The secrecy these states offer to account holders also brings up questions about whether money is intended for or came from illegal activity...

Gardner says that the national security concerns surrounding these revelations could and should spur Congress to create a national law that would essentially ban offering the level of anonymity that some states do in registering corporations. "Certainly if you've made [fighting terrorism] a major prong in public policy, as they have at the federal level, then they have a good claim for doing this," he said.

In Delaware... an investigative journalist recently set up a shell corporation for her cat...The News Journal also reported that Mexican drug lord Jaquin "el Chapo" Guzman is believed to have incorporated his tequila business in Delaware.