I researched a bit about the Friend's Day in Argentina and found this:
apparently it was created by iniciative of a man called Enrique Ernesto
Febbraro, who is a psychology teacher. He says that when he saw the
Moon landing in Jule 20th, 1969, he thought it would be a nice idea to
create a day to celebrate friendship around the world. So he sent a
thousand letters to different countries and received seven hundred
replies. It seems several political, religious and government agencies
supported the idea and it was quickly accepted and recognized in the
city of Buenos Aires. After a few time, it was recognized in the whole
country. And today it is celebrated in several countries.
My source:
http://www.prensarotaria.com.ar/es/diadelamigo.htm (It's in Spanish)