"This is the first leadership challenge to be fought out in this way and it's just the start," The Daily Star quoted a Westminster source, as saying.
"If Gordon Brown wants to stay leader and remain in Downing Street he has to make sites like Facebook and Twitter work for him," he added.
However, Brown's most famous rival is proving out to be in his cabinet itself, with way in front being Foreign Secretary David Miliband.
Facebook's 'David Miliband For PM' group has three times the number of supporters of his nearest rival, Education Secretary Ed Balls, who also has a thriving support group and who is one of Brown's closest allies.
"David is the best bet for leadership of the Labour Party and uniting the country. He's the only person who will make me vote for Labour," one supporter said.