2009-10: Teravainen skated for Jokerit Helsinki's U16 and U18 squads and also represented Finland internationally at the U16 level. Playing for the U16 team (C juniors), he scored 17 goals with 22 assists and had 14 penalty minutes in 12 games. In 12 playoff contests he scored 7 goals with 10 assists and 18 penalty minutes. Teravainen skated in 29 regular season games and four playoff contest for the U18 (B Juniors) team and scored 16 goals with 18 assists and 6 PIMs. In thirteen international contests for Finland he scored 7 goals with 10 assists.
2010-11: Teravainen spent the bulk of the season with Jokerit's U20 team, skating in four games for the U18 team, and also represented Finland at both the 2011 U18 World Junior Championship and the U17 World Hockey Challenge. Teravainen scored 3 goals with 17 assists and had 8 PIMs in 26 games for the U20 team. In eight A Juniors playoff games he scored 1 goals with 4 assists. In five games for Jokerit U18 (including one playoff game) he scored 1 goal with 4 assists. In the U18 WJC, he skated in six games for fifth-place Finland and was scoreless and minus-3 with 4 penalty minutes. At the U17 WHC he scored 2 goals with 5 assists in five games for Finland.
2011-12: Teravainen made his debut in Finland's SM-Liiga and skated in 40 games for Jokerit as a 17-year-old. He joined the men's team at Jokerit after a fast start with the club's U20 team. Teravainen also played three games with Kiekko-Vantaa in Mestis and played for Finland at the 2012 U18 World Hockey Championship. Teravainen's steady increase in ice time coincided with Jokerit's turnaround and he played a key role in the club's surprising playoff run to the SM-Liiga semifinals. During the regular season he finished with 11 goals and 7 assists and was minus-5 with 6 PIMs. In nine playoff games, he averaged over 15 minutes of ice time per game; scoring 2 goals with 4 assists and finishing plus-6. Jokerit defeated Espoo Blues in the bronze medal game. At the U18 WJC, Teravainen scored 2 goals with 6 assists and was plus-2 in six games as Finland advanced to the bronze medal game, falling to Canada in overtime. Teravainen was the second-ranked European skater in Central Scouting's final rankings prior to the 2012 NHL Draft.
A supremely skilled forward, Teravainen has the soft hands and hockey sense to be an offensive factor every time he touches the ice. He is an explosive skater and he uses his speed well to beat defenders one-on-one and create space for his linemates. His skillset is especially effective on the power play, where he is a talented distributor and can utilitze his heavy one-timer. He can also create well on the rush and make plays at high speed. His defensive zone play is not especially strong and, at 5'9 and 159 pounds, he will need to add strength before transitioning across the pond. After starting his draft year at left wing, Teravainen is expected to remain at center for Jokerit.
Teravainen will spend the 2012-13 season at the professional level in Finland's SM-liiga, centering a scoring line and playing a key role on the power play for Jokerit.