Mobile technologies have gradually changed people’s interpersonal communication habits, how to encourage elderly members to adopt mobile messaging apps (MMA) has merged as a critical issue in modern society. This study aims to empirically examine factors motivating the elders’ continuous use of MMA as a social support tool. According to the theory of planned behavior (TPB), the hypothesis of a factorial model of elders’ continuous use of MMA was developed. This study had collected a total of 519 valid samples from a field survey in northern Taiwan. A structural equation modeling approach was used to test the instruments and hypotheses. Results showed that all scales had acceptable validity and reliability, the model had a high fitness, and all hypotheses were supported. Attitudes, subjective norms, and perceived behavioral control significantly affect the elders’ continuous use of MMA. The external factors, interpersonal communication satisfaction, and enjoyment influencing attitudes respectively, social support influencing subjective norms, and adjustment to aging influencing perceived behavioral control, were all significantly effectual to TPB constructs. Based on the results, this study recommends that adult learning institutes and family members assist the elderly with positive adjustments to aging as well as increasing social involvements and interpersonal interactions through MMA. Furthermore, developing MMA with a simple interface and enjoyable experiences would be a plus for older adults.