The 17-year-old, who has made three pre-season appearances to date for the Pilgrims, has put pen-to-paper to complete his move from Sky Bet League One side Peterborough United.
Ravas, who has played for FK Senica and Spartak Myjava in his homeland, will turn 18 on August 16th.
Having already made his competitive debut against Lincoln City in the Lincolnshire Senior Cup, Ravas is expected to make his league bow against Stockport County on Saturday.