Police confirmed earlier today that the girl's disappearance had been reported to them and a spokeswoman said they were making inquiries in relation to the girl's whereabouts.
The sister said the girl had been talking to a man on the phone last night and quickly hung up and deleted her call history and contacts after her mother overheard the conversation.
After she went missing her mum checked the girl's Facebook account and found messages between her and an older man - who the family believe is aged 22 - dating back about two weeks.
"His Facebook page seems like a fake Facebook page as well. There's no photos," the sister said earlier.
The girl had replied to text messages from her worried family but wouldn't answer their calls, she told the Herald.
"She's been texting saying she was getting as far away from Whangarei as possible and to stop ringing her and get the police to stop looking for her."
The family believed she'd voluntarily gone with the man "but it's pretty messed up for someone that age to take an 11-year-old".
It was unclear whether the man knew how young the girl was but the sister said it would've been clear from her photos that she was younger than 16.
Running off was out of character for the girl, her sister said.
The family had "no idea" who the man was, she said, and believed the 11-year-old had never met him in person before.
