Colin Kroll, the co-founder of HQ Trivia and Vine, was found dead in his Manhattan apartment on Sunday.

Police responded to a 911 call for a welfare check at the Spring Street apartment on Sunday, a New York Police Department Spokesman told NBC News. Kroll was 34, police said.

Police found Kroll unconscious and unresponsive in a bedroom of the apartment, the spokesman said.

He was pronounced dead on the scene, police said.

A drug overdose is the suspected cause of death, police said, but an investigation is underway.

Kroll was named the chief executive of HQ Trivia, a phone-based trivia platform, in September. Prior to that, Kroll co-founded Vine, the popular short-form video service acquired in 2012 by Twitter. Vine was discontinued four years later.

"We learned today of the passing of our friend and founder, Colin Kroll, and it's with deep sadness that we say goodby," HQ Trivia said in a tweet Sunday. "Our thoughts go out to his family, friends and loved ones during this incredibly difficult time."