Both Chaoufi, the African Tour's number one rider, and Greek national time trial champion Tamouridis bring vital UCI ranking points with them which should help secure the Basque team's WorldTour status.
Chaoufi, 26, won the Moroccan road title this year and added a stage in the Tropicale Amissa Bongo in Gabo to his palmares.
Tamouridis, a time trial specialist, brings a wealth of experience to the team, having most recently competed at this summer's Olympic Games in London and the World Championships in the Netherlands.
The duo join nine other recent arrivals at Euskatel: Jon Aberasturi, Gari Bravo, Jure Kocjan, Juan José Lobato, Ricardo Mestre, Steffen Radochla, André Schulze, Alexander Serebryakov and Robert Vrecer.
Team manager Igor González de Galdeano said: "We want to be able to participate by right in the Tour de France and in the best races. That can only be achieved by being part of the WorldTour, which has its points' system.
"It's no longer a case of deserving to be in the WorldTour - that's not enough. You have to fulfil the requirements. There's no point wasting time by criticising the situation, the team, its decisions and the bodies that oversee this sport."