If a debtor moves to another country, you can probably still collect on a civil debt, but doing so might be so expensive that it is not worth your time. Also, the rules on proving a debt vary from country to country, so your home country and the debtor's new nation of residence play an important factor.
It is possible to collect on a debt in another country. In the U.S., for instance, the individual states often have agreements with other countries that let the state pursue delinquent alimony payments. Also, the U.S. has an obscure law called the Alien Tort Claims Act that lets citizens sue people for civil and criminal incidents that did not even happen on U.S. soil.
The biggest hurdle you will face when suing someone in another country is dealing with a foreign legal system. Since you probably do not know the ins and outs of this foreign legal system, you may have to pay thousands of dollars in legal fees for counsel. In the European Union, which is a loose alliance of almost all the countries in Europe, companies write off over $100 billion a year in bad debt because of the difficulty in suing companies and citizens that cross a border.
Locating the Debtor
Another major hurdle to collecting a debt from someone in a foreign country is locating the person. The debtor will have a new address, and you won't be able to track him with an identifying number like a Social Security number. Thus, you will probably have to hire a third-party to track the debtor down. In all, hunting a debtor abroad tends to cost at least half the balance on a debt, according Jen Haley of CNN.
One solution is to sell the debt to a debt collection agency. You will get pennies on the dollar, but it might be better than nothing, especially if it is a small debt. You can also ruin the debtor's credit, so if he does move back to your country, he is put in a position where he needs to pay or may not be able to obtain new credit. File a small claims case too. Some states in the U.S. allow a plaintiff to renew a judgment indefinitely.