Lost or Stolen Passport
Keep calm and (try to) carry on.
If you find yourself in the unfortunate position of needing to report a lost or stolen passport, contact ISOS. They will direct you to a nearby embassy or consulate to obtain a new one.
For American citizens:
U.S. Embassy in Moscow
Bolshoy Deviatinsky Pereulok No. 8
Moscow 121099
Russian Federation
Phone: +7 (495) 728-5000