Previous studies have indicated inconsistencies in utilizing the mobile application known as "WhatsApp" in academic vocabulary learning. This study attempts to overcome those inconsistencies by addressing three research aims, namely a) to examine any significant difference of employing vocabulary learning between using "WhatsApp"-based reporting and receiving on the one hand, and traditional-based reporting and receiving strategies on the other; (b) to determine the best predictor of vocabulary learning, and (c) to draw learners' attitudes among the four types of strategies. A mixed randomized experimental type of research with pre-test and post-test design as well as survey design has been consecutively applied for these purposes. The results of the study reveal that English Academic Purposes (EAP) learners who expand their academic vocabulary using "WhatsApp"-based reporting activities achieve better having been exposed to these three different treatments. Learners' endeavours to find out the mixed Indonesian-English vocabulary definitions by themselves, followed by reporting these to their teacher using "WhatsApp" turn out to be the best vocabulary learning predictor. Learners' attitudes observed in this cohort also show positive responses. Since the aspect of familiarity with academic vocabulary learning is not incorporated into this study, future researchers may find filling up this lacuna worth pursuing.