This is a difficult issue and a question that has been posed to us many times recently. Frankly, it is difficult and expensive to sue people in foreign countries. Some factors to consider:
– Do they have any business or personal connection to the United States? Property, corporation/LLC, advertising, clients, shipping, etc.? They have to have minimum contacts with the U.S. in order to be subject to the jurisdiction of U.S. courts. Otherwise, you have to sue them in their home country.
– Is there any property the defendant owns in the U.S. to recover money from or attach a lien to? Even if you can get a judgment in the U.S., you might not be able to collect anything in the U.S. if there is no property or business here. You will have to try and take the U.S. judgment to the foreign country and ask their courts to enforce it, often through another lawsuit. Some courts will, many will not.
Ultimately, we have to tell people that in most cases trying to litigate against a foreigner is not worth it – the damages have to be very large (ie. in excess of $150,000 USD) for it to be enticing for an American attorney. Even then, it should not be anticipated that the attorney would take such a case on a contingency basis (because of the risk and low chances of collecting, they will want to be paid hourly, not a percentage of the settlement).
If you do business with foreign companies or persons, be sure that your contract specifies an American venue for arbitration and litigation, and that both parties explicitly submit to U.S. jurisdiction.