CHRISTINA APPLEGATE's fiance has become the target of a vicious Twitter.com troll who is threatening to blow his head off.

Musician Martyn LeNoble has been subjected to menacing tweets from an anonymous account, prompting officials at the Los Angeles Police Department (LAPD) to launch an investigation.

Cops served a search warrant on Twitter HQ in San Francisco, six days after the horrifying messages emerged on 20 September (12). The profile has since been deleted, according to TMZ.com.

The hate-filled tweets read, "You stole (Christina) away from me. If not for you she would be mine... I will not accept this. I am going to kill you!!!!!!!!!... I'm going to bust your head in for taking her away from me!!! Be afraid, be very afraid!! You think this is a joke? I want to see how funny you think I am when I blow your f**king head off!!!"