Music industry insiders point out that Kim's death puts the spotlight on the pressures piled on young Korean pop stars as they chase after success and fame.
Kim alludes to the pressures of living in the spotlight in his note: "I guess I was not meant to lead a life in the public eye. That's why it was hard. Confronting the world, and being in the public eye. Why did I make those decisions. It's ridiculous."
Back in 2011, rapper G-Dragon talked about being depressed after he was accused of plagiarism while singer and actor Jeong Jin Woon from 2AM revealed that he suffered from depression after his group's American tour in 2010.
Says Mr Alan Chan, director of home-grown talent company Big Boss Asia, which is behind Singapore's first K-pop group SKarf: "(Kim's) death speaks volumes about the pressures that South Korean artists face as the industry is so competitive. New artists are constantly replacing the old ones."
He adds that many South Korean artists suffer from depression and that the suicide rate among them seems higher compared with their counterparts from Hong Kong or Taiwan.
"I guess one way to overcome the pressure is to leave the industry or find some way to relax. But this is easier said than done."
Mr James Kang, a former marketing director at Warner Music Singapore, says Kim was "a quiet and diligent artist who delighted in performing and meeting his fans" and "seemed cheerful and sparkled on stage".
In 2010, he worked on two SHINee fan meets here as well as other activities to promote the band's EP, titled 2009, Year Of Us.
"In my opinion, there are too many unknown factors behind an artist's suicide," he says. He is now director of Mode Entertainment, which has brought in K-pop artists Eric Nam, Baek Ji Young and Kim Jong Kook.
"Pressure from the industry could definitely be one of them, as they struggle to manage the market's expectations of them, as well as their own expectations of themselves."
He adds that artists should always have someone to speak to about stress, be it their management, peers within the industry or friends and family.
"The artists must always feel that they are not alone," he adds.
As the official SHINee social media accounts changed their profile photos to black squares or circles, fans online shared their grief by writing tributes and using hashtags such as #RosesForJonghyun.
Many are still stunned by the news of his sudden death.
The members of a local group of SHINee fans who call themselves Forever_SHINee recall seeing the singer in a good mood when he was in Singapore last month.
The group's spokesman, who wants to be identified only as Ning, says: "When SHINee visited Singapore for the Shilla Beauty concert last month, we had the opportunity to meet them at the press conference and watch their stage performances.
"Jonghyun was extremely friendly, smiley and talkative. As fans who have watched him for the past eight years, we know he does not like the summer and being in the hot weather, we were surprised that he kept his enthusiasm till the end for Singapore fans."
Several of the group members also travelled to Seoul to watch his solo concert on Dec 9 and 10.