The following is the US position on dual citizenship/retaining US citizenship. You can only renounce your US citizenship if you tell the US directly. See excerpts below.
Administrative Presumption of Intent to Retain U.S. Citizenship
…The Department has adopted an administrative presumption that U.S. nationals intend to retain United States nationality when they: obtain naturalization in a foreign state (INA 349 (a)(1)); declare their allegiance to a foreign state (INA 349(a)(2)); … In accordance with the administrative presumption, when an individual commits one of the foregoing acts, that person will retain U.S. nationality unless he or she affirmatively, explicitly, and unequivocally asserts an intention to relinquish such nationality.
Disposition of Cases when Administrative Presumption is Applicable
When, as the result of an individual's inquiry or an individual's application for a passport it comes to the attention of a U.S. consular officer that a U.S. national has performed an act made potentially expatriating …, the consular officer will simply ask the applicant if he/she intended to relinquish U.S. nationality when performing the act. If the answer is no, the consular officer will record that it was not the person's intent to relinquish U.S. nationality and, consequently, find that the person has retained U.S. nationality.
Reference: https://travel.state.gov/content/travel … ality.html