^rsbm
As we've seen in other cases, a lot of messaging apps (FB Messenger, WhatsApp, Signal, Snapchat, etc.) use data, rather than cellular minutes or text messages, and are much harder/impossible to track (the warrants take months). Mekayla Bali is one such case; CCTV shows her seeming to communicate with/waiting for someone throughout the day before she disappeared.
Kik (mentioned on Maddie's Quora profile) also comes up in the Bali case; at the time, police were sounding the alarm about it having few parental controls and strangers to contact others without connecting/being "friends." (
source)