According to a survey conducted by the Korea Creative Content Agency in 2018, the gaming usage rate of Korean youth was 91.9%, and video games have become the number one leisure activity [1]. Although video games have become widespread and famous, the potential negative impact of video games as a leisure activity on the player base has been a concern for the general public. Numerous studies have pointed to an inverse association between video games and adolescent mental health [2]. The most direct effect of the time adolescents spend on video games is away from real-life interpersonal interactions, which can exacerbate social relationships and lead to feelings of isolation [3]. Therefore, the development of loneliness is expected in adolescents who enjoy playing games.

Loneliness in adolescence can be defined as distress brought about by one's own frustrated need for social and emotional interaction with others and negative evaluations of social relationships [4]. Some studies have shown that loneliness is high among Korean adolescents [5]. Moreover, adolescents with high levels of loneliness are likely to experience various maladaptive problems such as depression, anxiety, suicide, smoking, drinking, and failure in school due to feelings of despair, misanthropy, and powerlessness [6].

While most previous research has focused on the causes and mechanisms that may underlie the development of loneliness, the trajectory of change in loneliness has been less studied within Korea, especially among high-risk groups such as game players. Adolescence is a time of dramatic physical and psychological change, and loneliness may exhibit a high degree of instability [7]. Therefore, there is a need to explore the trajectory of adolescent game players' loneliness over time to understand the mental health of adolescents. The research question in this study is, how does loneliness among adolescent game players change over time? 

This study aims to analyze how loneliness among adolescent game players changes over time. The loneliness of adolescent game players shows a quadratic growth trajectory of change over time that increases and then decreases. There are significant individual differences in the initial values and rates of loneliness change. There are significant correlations between linear and non-linear rates but no statistically significant relationship between initial value and rate of change. This is not the same as most current researches showing that loneliness increases linearly through adolescence. The trajectory of change in loneliness of the participants in this study took the trend of increasing and then decreasing, possibly because the positive attitude towards being alone during adolescence increased with age [9]. Specifically, adolescent game players may be more affected by being alone in the early years, so loneliness is always on the rise. However, by late adolescence, when adolescence is no longer afraid of being alone and has learned to appreciate the positive aspects of being alone, playing alone does not feel as lonely as it used to. Thus, feelings of loneliness slowly begin to diminish. This is similar to the findings of van Dulmen and Goossens [10]. Adolescent game players are a high-risk group for loneliness, and social workers should develop intervention services based on the timing and characteristics of changes in their loneliness to improve their effectiveness.