After the COVID-19 pandemic, a surge in new stock investors, motivated by the pursuit of alternative income, fear of missing out, and social media influence, has heightened global stock market activity. This surge underscored the necessity of online stockbrokers as streamlined platforms for facilitating communications with investors and executing their transactions. This study investigates the adoption of online stockbrokers among Indonesian investors, focusing on both desktop and mobile users to provide a holistic understanding of the domain. Extending the Unified Theory of Acceptance and Use of Technology framework with additional constructs - System Quality, Perceived Reputation, Trust, Risk, and Price Value - this research examines diverse factors influencing investor adoption. Using survey data from 143 investors and analyzing it with Partial Least Squares-Structural Equation Modeling, the study identifies the pivotal roles of performance expectancy, system quality, and social dynamics like perceived reputation and social influence as significant predictors of adoption. The findings reflect a shift from traditional, personalized stockbroker interactions to accessible, efficient digital platforms and emphasize the critical role of social dynamics in driving the adoption of financial services. Lastly, the study offers theoretical insights and practical recommendations for advancing financial services, particularly in contexts where users prioritize high complexity and feature-rich platforms, by highlighting the critical factors driving online stockbroker adoption.