She tweeted: "To the person who mugged my 67 year old mum and my sister. I hope you get hit by a bus and die. Slowly."
The message received more than 160 retweets and messages from other celebrities including fellow presenter Kate Thornton, Spice Girl Emma Bunton and actress Martine McCutcheon.
This isn't the first time Myleene, 35, has had a brush with violent street crime.
The mum-of-two was herself described as "very shaken up" after she was attacked by a gang in Bermondsey, south London, in 2005.
She was pushed to the ground and had a bag of chips dropped on her head as teens tried to take photos of the terrified star.
Myleene gave no further details of the alleged attack on her mum and sister.