Pekturk joined the club from Eintracht Trier in 2010 but the 24-year-old midfielder has moved on to join Istanbul BB in the Turkish top flight.
And the exit of 25-year-old Mikkelsen to Rosenborg comes just six months after he joined the club from Danish champions Nordsjaelland.
But Greuther Furth general manager Rouven Schroder admits that the Denmark international winger struggled to make an impact.
"Unfortunately Tobias has been unable to breakthrough in the Bundesliga," he told Deutsche Presseagentur.
"He did not make the development and progress we had hoped he would. It was not a successful spell for him or for us."