The Saturdays singer, who broke up with Poynter in November, has been sent abusive messages on Twitter.
The 22-year-old is said to be terrified by the vicious tweets Poynter supporters have written, according to Now magazine.
One tweet read: "You're a f**king bitch. I, along with many other mcfly (sic) fans, hope you die and rot in a hole."
Another user of the microblogging site threatened: "I will hunt you down and kill you."
The McFly singer completed a stint in rehab after finding it hard to deal with Sandford being in a relationship with footballer Wayne Bridge.
Poynter's bandmate Danny Jones recently claimed that he does not believe Sandford and Bridge will last as a couple, adding that he "couldn't give a s**t what she does".