She captioned the post: “Today has been a year without you baby brother. I miss you endlessly every day.”
The 32-year-old actress also shared a collage of childhood photos on her Instagram Story, but didn’t include a caption, and reposted other tributes made in honour of her brother.
The ‘Runaways’ star admitted earlier this month she wished she’d hugged her brother “properly” the last time she saw him.
Sharing a throwback photo of her and her brother on her Instagram Story, she wrote: “A year ago this morning was the last time I got to see you.
“I didn’t hug you properly because I thought you had COVID. I wish I’d hugged you properly. I miss you every day.”
Riley recently admitted she still has “hard days” as she grieves for her brother but she’s doing her best to live in the moment and be appreciative of the good things in her life.
She said: “I’m really consciously trying to be present, and not use anything as any kind of escape, and be cognisant of when I’m doing that.
“I’m just generally trying to be grateful for everything at the moment, trying to operate in love, and keep my heart open, and give and receive love.
“And not in a woo-woo way, because I definitely have hard days, and all kinds of pain and suffering and all that.
“But I think when you realise that’s part of it, and your expectation isn’t to just be feeling joy, that’s been a real shift for me in finding those moments and things to smile about.”