D'Amigo represented the under-18 United States team for the first time in his career at the 2009 IIHF World U18 Championships, where he helped them win the gold medal and led Team USA in scoring; he was also fifth overall in tournament scoring, with 13 points. He represented the United States at the junior level at the 2010 World Junior Ice Hockey Championships, where he won gold and finished fourth in tournament scoring, with 12 points. He represented the U.S. at the junior level once again at the 2011 World Junior Ice Hockey Championships, where he won bronze and finished with two points scored.