 Moon began playing football at a young age for local boys' club sides Bankfoot and Fossoway.He then joined the St. Johnstone youth set-up and was coached by then Head of Youth Development, Alastair Stevenson and his successor, Tommy Campbell.Moon had played at youth level for St Johnstone and was a big part of the very successful under-17 side in the 2003–04 season, and that prompted then-manager John Connolly to give him his first professional contract in the summer of 2004.