Wherever people knew him or admired his renowned family, a somber mood fell Saturday.
Retired astronaut Buzz Aldrin, the second man to walk on the moon, took a moment to offer his sentiments at an Apollo 11 anniversary celebration at Kennedy Space Center, named after JFK Jr.'s father, who insisted the American space program go forward.
"Our hearts go out to the family who has started so much, achieved so much, suffered and sacrificed so much and now has even further uncertainty," Aldrin said.
Kennedy and his wife, Carolyn Bessette Kennedy, and her sister, Lauren, were missing aboard a plane that left New Jersey on Friday evening, bound for a family wedding Saturday in Hyannisport, Mass.
Singer Michael Jackson, among the invited guests, sent a message of sympathy. In Chicago, the Sun-Times published an "Extra Edition" of its Sunday paper on Saturday afternoon: "JFK JR.'S PLANE MISSING."
"When the storms of life come suddenly, we must not panic. We must not question the goodness of God," said the Rev. Jesse Jackson.
At New York's Yankee Stadium, before an afternoon game against the Atlanta Braves, Yankees announcer Bob Sheppard invoked a moment of silent prayer.
"The Kennedy family has done so much for our country," Sheppard said. JFK Jr. watched another Yankees-Braves game from a front-row Yankee Stadium box Thursday night.
The Rev. Billy Graham called JFK Jr. a "personal friend" and encouraged people everywhere to pray. "It is my prayer that, if it is God's will, they will be found alive and well," Graham said.
Sen. Orrin Hatch, R-Utah, a close friend of Democratic Sen. Ted Kennedy, D-Mass., said Saturday he was "praying there is some simple answer."
"JFK Jr. was doing everything right. He got his law degree, worked as a prosecutor, started George," Hatch said. "I expected sometime in the future he would definitely have gotten into politics."
Douglas Brinkley, a University of New Orleans history professor and a contributing editor at George, the magazine founded and edited by JFK Jr., spent Saturday trading consolations with friends.
"Pragmatically, it looks bleak," Brinkley said. But he tried to retain hope.
"John had a great sense of humor and sense of self-deprecation and a trickster side of him," Brinkley said. "I keep hoping his being missing is greatly exaggerated and he'll appear in Nova Scotia or Maine."
Brinkley called Kennedy a "terrific editor" and a liberal Democrat whose heroes included the Rev. Martin Luther King Jr., Czech president Vaclav Havel and farm-labor leader Cesar Chavez.
"He was circling around hw he could best enter the public arena as a reformer," Brinkley said.
As Kristen Helm basked in the sun outside of a trendy Denver coffeehouse, friends told her Kennedy was missing. Helm, 33, a sales representative, has been fascinated with the Kennedys for most of her life. "I cried when Jackie O. [Onassis] died and I had no association with her," she said.
But, she said, "Quite frankly, I'm not surprised. I really believe that the Kennedys have a legacy of bad omens."