A young man described as “happy, bright and full of hope” tumbled to his death from his 24th-floor balcony in Midtown — possibly after the railing gave way, sources said yesterday.

Neither his friends nor investigators seem to believe that Connor Donohue, 24, jumped from the East 39th Street building Sunday morning.

“He was happy, bright and full of hope. He had a great sense of humor and got along with everybody,” said Mekaelia Davis, a fellow volunteer at the Young Nonprofit Professionals Network.

Donohue had been a dean of students at Prep for Prep, a nonprofit that helps New York students gain admission to elite high schools nationwide.

A part of the railing also fell, prompting a Department of Buildings spokesman to say, “A post was loose or may have been damaged prior to the incident.”