MADRID, Feb 3 — Spain and Greece on Tuesday proposed bans on social media use by teenagers, marking a hardening of attitudes by European nations against technology platforms they say are designed to be addictive and which can expose children to harmful content. Spain wants to prohibit social media for those aged under 16, Prime Minister Pedro Sanchez said on Tuesday. Greece is close to announcing a similar ban for children under 15, a senior government source said. They join a host of countries