The 34-year-old Frings and 32-year-old Koevermans became two of the club's "designated players" who are paid mainly outside the team's salary cap and will begin playing after July 15 when the MLS transfer window opens.
"We have added two very important players with significant experience and technical ability," Toronto head coach Aron Winter said in a statement.
"Torsten and Danny will make an immediate impact at our club. Signing Torsten and Danny is a very important step in building a team that our fans are proud to support."
Frings won 79 caps for Germany, scoring 10 goals, and played at the 2002 and 2006 World Cups and Euro 2008.
He was in the team who lost the 2002 World Cup Final to Brazil and the Euro 2008 Final to Spain.
He turned down the offer of a coaching role at Werder Bremen, the Bundesliga club where he spent most of his career including last season, to extend his playing days with a move to the MLS.
Koevermans, who had spells at Sparta Rotterdam, AZ Alkmaar and most recently PSV Eindhoven, has won four Netherlands caps.
Financial terms of the deals were not disclosed with the club saying simply that the players had signed "multi-year" contracts.
MLS clubs are allowed to sign up to three "designated players" enabling them to bring top international names to the league such as LA Galaxy's David Beckham.
