"I'm gonna carry this torch for you brother, with a forced smile on my face and Im gonna open my heart just cause your telling me to," the Fast and Furious star wrote on her Facebook page.
Meanwhile, Diesel, who co-stars in the film franchise as well, posted a quote by Scottish poet Thomas Campbell on his Facebook page to honor his late friend.
"To live in the hearts we leave behind, is not to die. Thomas Campbell," he wrote. "Pablo, I wish you could see the world right now... and the profound impact, your full life has had on it, on Us...on me..."
"I will always love you Brian, as the brother you were... on and off screen."
The 46-year-old actor also talked to mourners at the site where Walker lost his life, saying over a loudspeaker, "If he could see for himself that all of you have showed up to show my brother love at this hard time, and the family gets to see all of you show the love that you've shown Paul, it's going to stay with me forever," according to KTLA-TV.
"I just wanted to say thank you," he continued. "Thank you for coming down here and showing that angel up in heaven how much you appreciated him."
Walker and his friend Roger Rodas died Saturday after the 2005 Porsche Carrera GT they were riding in crashed into a pole and caught fire in Santa Clarita, Calif.