Adoption rates of parental control applications ("apps") for teens' mobile devices are low, but little is known about the characteristics of parents (or teens) who use these apps. We conducted a web-based survey of 215 parents and their teens (ages 13-17) using two separate logistic regression models (parent and teen) to examine the factors that predicted parental use of technical monitoring apps on their teens' mobile devices. Both parent and teen models confirmed that low autonomy granting (e.g., authoritarian) parents were the most likely to use parental control apps. The teen model revealed additional nuance, indicating that teens who were victimized online and had peer problems were more likely to be monitored by their parents. Overall, increased parental control was associated with more (not fewer) online risks. We discuss the implications of these findings and provide design recommendations for mobile apps that promote online safety through engaged, instead of restrictive, parenting.