The actor - who was famed for his role of Kenickie in the 1978 musical film - died last month at the age of 60 after a reported drug overdose and his friends and family attended a service at the Our Lady Of Grace Church in Encino, California, to remember him.
'Lost Boys' star Corey - who was friends with Jeff for 25 years - told the congregation: "Jeff was an amazing leader. He had a light inside of him that was so inspiring to many. I was one of those people that he affected so profoundly.
"He had energy, he had charisma, he had joy and laughter in his heart. And what he wanted more than anything was to share that - with as many people as he could."
Guests also signed purple balloons - Jeff's favourite colour - and released them to go up in the sky in unison.
Throughout his life, Jeff - who had a grown-up son Emerson with his ex-wife, 'Grease' co-star Olivia Newton-John's sister Rona - battled drink and drug addictions and in the 80s he was treated for a substance abuse problem.
In 2008, he signed up for 'Celebrity Rehab with Dr. Drew' and spoke candidly about his addictions to cocaine, alcohol and painkillers.
Following his death, John Travolta - who played Danny in 'Grease' - described Jeff as a "wonderful and decent man".
He added: "My heartfelt thoughts are with his family and loved ones at this very difficult time."