2008-09: Andreoff skated in 66 games for Oshawa in his first full season in the OHL. After appearing in 25 games with the Generals in the previous season, he scored 11 goals with 14 assists and was -13 with 37 PMs as Oshawa finished fourth in its division and missed the OHL playoffs. Andreoff scored 5 of his 11 goals on the power play. Andreoff was ranked 168th amongst North American skaters in Central Scouting's final rankings but was not selected in the 2009 NHL Draft.
2009-10: Andreoff scored 15 goals with 33 assists and was -18 with 70 PMs in 67 games in his second season with Oshawa. The Generals again missed the OHL playoffs, finishing fourth in the East Division but six points behind the Central Division's fifth-place Sudbury Wolves.
2010-11: Andreoff had a break out season both physically and offensively as the Oshawa Generals were one of the big turnaround stories in the OHL. Andreoff was the Generals' second-leading scorer with 33 goals and 42 assists and led Oshawa in both plus/minus (+34) and penalty minutes (109). After missing the playoffs in back-to-back seasons, the Generals finished second in the East Division and won a first round playoff series. In 10 playoff games Andreoff scored 3 goals with 8 assists and was +3 with 16 PMs. The Kings selected Andreoff in the third round (80th overall) of the 2011 NHL Draft.
2011-12: Andreoff signed a three-year entry-level contract with the Kings in October 2011 and made his pro hockey debut with Los Angeles AHL affiliate Manchester at the end of the year following his fourth season with OHL Oshawa. He joined the Monarchs for the last five games of the season — scoring his first professional goal (his only point) and was an even plus/minus with 4 penalty minutes. Manchester finished second in the Atlantic Division and lost to Norfolk three games to one in a first round playoff series. Andreoff scored 2 goals and was minus-four with 2 penalty minutes in 4 playoff games. He scored 22 goals with 36 assists and was plus-one with 88 penalty minutes in 57 games for the Generals. In six playoff games he scored 1 goal with 3 assists and was minus-six with 4 penalty minutes. He was with the Kings during their Stanley Cup run but did not appear in any games.
Andreoff signed a three-year deal with the Kings and is playing for the Oshawa Generals for the 2011-12 season.