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.
U.S. Embassy Brasília
SES - Av. das Nações, Quadra 801, Lote 03
70403-900 - Brasília, DF
Phone: (55-61) 3312-7000
Fax: (55-61) 3225-9136
Embassy FAQ