Colin Kroll, the co-founder of the HQ Trivia app and Vine, has been found dead in his New York apartment.
Mr Kroll, 35, was discovered by police who were called to his lower Manhattan home by the tech entrepreneur's girlfriend soon after midnight on Sunday.
She had been unable to raise him on the phone and asked officers to carry out a welfare check.
When police arrived at his apartment on Spring Street near the Soho district, they found him unconscious and unresponsive on his bed.
Celebrity website TMZ said there was "drug paraphernalia nearby", and that he had died of an apparent overdose.
He was pronounced dead at the scene, with the cause of death to be determined by a medical examiner.
Mr Kroll was the chief executive of the real-time trivia game app, which live-streams short trivia shows to users and became popular after its release in 2017.
It reached the top of Apple's free game app chart in the first couple months of 2018 but has since fallen out of the top 100 free games list on the iTunes app store.
In 2012, Mr Kroll was part of the team that invented short-form video platform Vine, and followed the company when it was bought by Twitter.
He was sacked by Twitter and in 2017, he and business partner Rus Yusupov formed Intermedia Labs, the company behind HQ Trivia.
So sad to hear about the passing of my friend and co-founder Colin Kroll. My thoughts & prayers go out to his loved ones. I will forever remember him for his kind soul and big heart. He made the world and internet a better place. Rest in peace, brother.
— Rus (@rus) December 16, 2018
Mr Yusupov tweeted his sadness, saying his "brother" had a "kind soul and big heart… made the world and internet a better place."
We learned today of the passing of our friend and founder, Colin Kroll, and it's with deep sadness that we say goodbye. Our thoughts go out to his family, friends and loved ones during this incredibly difficult time.
— HQ Trivia (@hqtrivia) December 16, 2018
HQ Trivia's Twitter account also shared a message of condolence, describing its "deep sadness".
Intermedia Labs is reportedly in turmoil as it has struggled to find a new audience and in October launched a new game, HQ Words.
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