Adoptees adopted outside the United States or internationally face different challenges in searching for their birth parents. Each country has its own laws governing the information and access to it. In addition the record keeping practices vary across the countries and cultures and you may find that no information has been ever recorded or that records were misplaced or that cultural practices placed no emphasis on accurate record keeping.

However, I have a theory that it may actually be easier to gain access to an original birth certificate in a foreign country than it is in the United States since some countries do not seal their vital records.
I am not well versed in international adoption search but I felt that it should be addressed. I will try and do my best to get you started. Feel free to make suggestions and comments as this is un-chartered waters for me.

I think that the first thing the adoptee should do is contact the agency that facilitated the international adoption. I believe that the US agency should be able to share the name and location of the agency or orphanage abroad and perhaps the names of the caregivers, attorneys or others involved in the placement or adoption. The agency may be able to provide specific information on names, dates, and places. They also may be able to offer some medical history, biographical information and circumstances regarding the adoption.

If you are seeking documents such as a birth certificate the US or foreign child placing agency is not able to provide, I suggest applying to the government agencies in the birth country. Address of offices that maintain vital records in foreign countries can be found at the US State Department website.

If you are initiating an international search you can try contacting the US Citizenship and Immigration services to receive copies of the immigration records.

In writing this I found an organization called International Social Services which can help adoptees find their birth family internationally. The website is www.iss-usa.org.

There are also support groups for adoptees adopted internationally. They can provide information on searching. I know that the countries that have placed a large number of children with families in the US such as Korea, have support groups and organizations with websites and search information.

I do think that searching internationally is more difficult than searching in the US. If your search is unsuccessful, you may want to visit your birth country and experience your birth culture. Visiting your birth country may provide some satisfaction.