Casey Johnson friends mourn on Twitter

Casey Johnson's friends have taken to Twitter to pay tribute to the late heiress following her death yesterday.

According to People, the Hilton sisters and Johnson's fiancee Tila Tequila are among those leaving tweets.

"R.I.P my Angel," Tequila said. "u will forever be in my heart! I love u so so much and we will Marry when I see U in Heaven my Wifey (sic)."

Paris and Nicky Hilton are said to have known Johnson since they were babies. "In bed crying, looking at baby pictures of Casey, Nicky and I. I feel so upset. I feel like I've lost a sister. My heart is broken," Paris wrote.

Lindsay Lohan also shared her thoughts, saying: "R.I.P. To a friend to and of many - Casey Johnson - my regards to her family, friends and her beautiful daughter Ava* you are in our hearts CJ."

Police were called to a house in Los Angeles on Monday morning, where they found Johnson dead at the scene. There was reportedly no evidence of foul play. A toxicology report is forthcoming.