Two of the killers, who were all aged 17 at the time, were then caught on camera celebrating with a fist-bump.
Danish Mansha, Daiyaan Arif and Rimsha Tariq killed Sohail Ali after finding him online and enticing him to Summerfield Park on the outskirts of Birmingham last year.
Mansha and Tariq, both from Birmingham, were found guilty of murder while Arif, from Oldbury, was convicted of manslaughter.
#WATCH | Two killers fist bump after a man was lured to a #Birmingham park and stabbed to death.— West Midlands Police (@WMPolice) November 5, 2021
Three teens used the internet to find someone who they believed wanted to have violent sex with women and enticed him to his death.
Full story 👉 https://t.co/qXRt6ATVgB pic.twitter.com/VtG6twJEYs
The teenage killers targeted 29-year-old Mr Ali believing that he wanted to have violent sex with women, West Midlands Police said.
The victim had been speaking with Tariq online before agreeing to meet her in the park where Mansha, armed with a knife and a blank firing gun, and Arif were lying in wait.
Mr Ali was stabbed seven times and shot, with the attack using such force that the knife snapped and part of the blade was found embedded in his chest.
He was ambushed at Summerfield Park, on the border of Birmingham and Warley, at around 2.30pm on December 4 and died in hospital just after midnight.
Video footage shows Mansha and Arif celebrating with a fist-bump in the aftermath of the killing.
While Mansha was the one armed, all three were charged with murder under joint enterprise after digital forensic experts examined their mobile phones.
The teenagers had been in regular contact with each other in the days leading up to the killing and Tariq continued to chat to Mr Ali via WhatsApp and Instagram up until half an hour before he was killed.
The three suspects denied murder and after a 10-week trial at Coventry Crown Court, Mansha and Tariq were found guilty of murder, while Arif was convicted of manslaughter. Mansha was also found guilty of possession of a bladed article. The killers, who are all now aged 18, were sentenced on Thursday
Mansha, of Majuba Road, Birmingham, was jailed for life with a minimum of 19 years
Tariq of Bevington Road, Birmingham, was jailed for life with a minimum of nine years
Arif, of Apsley Road, Oldbury, was jailed for three years and six months
Following the sentencing, Mr Ali's family said: “We are pleased that the defendants were found guilty and sentenced today for the brutal crime they committed. Sadly nothing can bring Sohail back to us.
“Sohail was murdered needlessly and his life has been stolen from him. The pain that we suffer from his loss is overwhelming. He will forever remain in our hearts.
“We are truly grateful and thankful to the police and legal team who worked so hard on my son Sohail's case to get him justice.”
Detective Inspector Laura Harrison, from the West Midlands Police homicide team, described the case as "really sad".
She added: "It was a completely senseless attack that took a life and changed three more forever.
“My officers have worked tirelessly on the case; and although today's verdict can never bring Sohail back, I am pleased that we have been able to secure justice for him and his family. My thoughts are with them at this time.”