According to police, his family said Bevacqua had no known serious medical conditions.
Bevacqua started LRG — commonly worn by celebrities, hip-hop musicians, athletes and skaters — with friend Robert Wright in 1999. By 2007, Entrepreneur Magazine named them No. 5 in its Hot 500 list, citing 2006 sales figures at $150 million.
His fiancé had been out of town for the weekend and had last spoken to him Sunday night.
Ben Baller, a Los Angeles-based jeweler and friend of Bevacqua, expressed his feelings on Twitter on Tuesday, saying it was "the worst news I've heard in my lifetime … "
Thousands of fans took to Twitter, sending their condolences and marking them with the hashtag #RIPJonas.
LRG turned its website into a memorial for its founder, with cofounders Wright and Charlie Moothart expressing their loss. All other uses for the site, including shopping, weren't accessible Wednesday.
"Yesterday, we lost an icon," the site stated. "As co-founder of LRG, Jonas was a creative visionary, loved by those around him. Jonas was a friend, partner, father, mentor and a very caring person who inspired so many of who were fortunate enough to be around him."
It goes on: "There is a hole in our hearts that will never be filled … He is in a better place and will be watching over us always."
Calls to LRG's Irvine headquarters were not returned.
According to Wright and Moothart's statement, Bevacqua is survived by his fiancé, son, seven siblings, mother and father.