City's defence of the title came to an end on Monday night as United beat Aston Villa to claim their 20th championship.
"There has to be a determination amongst ourselves," Platt told Sky Sports News. "It is not good when you hurt, when you lose it.
"When you set a season off and you think that you have an opportunity to win it like we did, and like they did last year, that feeling, that hurt is much deeper and more profound than when you win it."
Manchester City continue their league campaign on Saturday when they welcome West Ham United to the Etihad Stadium.