In the evolving landscape of user-generated content (UGC) platforms, where videos have become a preferred mode of entertainment and information consumption, the importance of thumbnails in attracting viewers cannot be overstated. This study delves into the intricate relationship between thumbnail design and video success, focusing on the Chinese UGC platform RED. Specifically, the research examines the thumbnails of @Amber Lulu, a vlogger with a consistent style of video and thumbnails. Analyzing a data sample of 30 videos within the "day in my life vlog" category, the study categorizes thumbnails based on three design elements: emphasis on one person vs. a group, two lines of title vs. one line, and a close vs. far background. The results reveal significant correlations between thumbnail design and video metrics, notably emphasizing the positive impact of a distant background, an emphasis on one person, and the use of two lines of heading. Drawing from communication theories such as visual hierarchy, cognitive load theory, and the effect of image characteristics, the study provides valuable insights for content creators seeking to optimize their thumbnails for increased engagement. This research contributes to a nuanced understanding of the role thumbnails play in viewer engagement on UGC platforms, offering practical advice for content creators to design more visually appealing thumbnails for their videos.