Web 2.0 applications with multimedia affordances provide a creative way to expose students to a non-threatening environment for practising English. Motivated by the potentials of this type of application for English speaking instruction, this study aimed to examine the effects of high school learners’ self-practice using an app called Voki on their speaking performance. A quasi-experimental control group design was employed, in which the effect was measured by means of two speaking tests before and after the treatment, and further explored with a semi-structured interview. The results showed the increase in the students’speaking skills and the satisfaction with this Web 2.0 tool for its effectiveness and engagement. Their shyness and nervousness about uttering the target language diminished as their confidence increased. Accordingly, more evidence of the efficacy of Voki on EFL learners’ speaking performance was offered in the study. Future research can investigate learners’ improvement in language proficiency in different skills and contexts and involve larger sample sizes.