Hazel didn't have traditional social media accounts because she didn't know enough people to bother. Aside from her art blog on Tumblr and accounts on a few other sites where artists could showcase/be paid for their art, she only had an Instagram account advertising what she sold on her Etsy page.
Will had been driven slightly crazy during their years apart once social media became popular and he wasn't able to find her anywhere. A year after the social media craze originally hit and no luck finding her, he became so worried he actually headed up to the Bay Area to check on her.
Before escaping the mental hospital he had been sure to peek at Hazel's records that were lying around in the head shrink's office so he knew her last name and the address of her legal guardian.
Hazel Dixon, age eight, whose uncle lived nearby in San Francisco and had never once bothered to either call or visit her while she was locked up. What a scumbag. He wasn't worthy of being Hazel's guardian.