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Kim Zolciak-Biermann and her daughter Brielle are mourning the death of a family friend.
The Don't Be Tardy stars paid tribute to Ethan McCallister, who died on Saturday at 28 years old. "We will miss your huge beautiful smile, constant jokes, cowboy boots and infamous shirts," Kim, 42, wrote on Instagram.
"You were always the life of the party!! One of the most genuine kind hearted people I have ever known," she continued. "Always willing to help anyone anywhere. We love you Ethan and I will make sure justice is served."
McCallister was struck by a vehicle at Piedmont Avenue and Lindbergh Drive in Atlanta, as he was out walking at about 3 a.m. local time, according to WSB-TV, which reported that police are searching for the suspect, who left the scene, driving a dark-colored Range Rover.
A spokesperson for the Fulton County Police Department did not immediately respond to PEOPLE's request for comment.
Meanwhile, Brielle, 24, shared some throwback photos with her "best friend" McCallister, who recently vacationed with her and some friends in the Bahamas. "Ethan.... I can't believe I'm even writing this. I'm sick sick sick to my stomach," she wrote in the caption.
"You are my happiness my joy my light in this very dark world.. the life of the party and the sweetest soul I've been blessed to know," she continued. "You are my best friend. My heart. My everything. There will never be another you. Ever ever ever. You came into this world with 1 mission... make people smile. You were damn good at it too. There was never a moment I wasn't laughing with you!!"
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"We haven't spent a weekend apart all year!!! How am I supposed to go anywhere without you? How am I supposed to laugh, smile, GO TO MIAMI OR DRINK 1942 WITHOUT YOU!? God I love you ethan. I really really do. I can't wait to see you again," Brielle wrote.
Kim and Brielle asked their combined 4.4 million Instagram followers for help in identifying the driver, also sharing a link to the family's GoFundMe to cover costs for his funeral.