"I miss L'Wren so much and I am so sad she isn't here anymore," she wrote alongside a picture of the them together at an event at the Serpentine gallery last summer.
"She was such a big part of my life. I will never forget all the fun times we had together. She was part of our family and always will be. Rest in peace."
Last month, Mick released a statement admitting he was struggling to come to terms with the news that the fashion designer had taken her own life.
"I am still struggling to understand how my lover and best friend could end her life in this tragic way," he wrote in a message on his website entitled 'L'Wren'
"We spent many wonderful years together and had made a great life for ourselves. She had great presence and her talent was much admired, not least by me.
"I have been touched by the tributes that people have paid to her, and also the personal messages of support that I have received."
Concluding, he said, "I will never forget her."
The rock legend's note came just 24 hours after it was revealed that L'Wren had been found in her Manhattan apartment.