Second language learners are typically hampered by the lack of a natural environment to use the target language for authentic communication purpose (as a means for "learning by applying"). Thus, we propose MyCLOUD, a mobile-assisted seamless language learning approach that aims to nurture a second language social network that bridges formal classroom learning and informal use of the language. The research context that we have applied MyCLOUD to is Chinese as a second language learning. In this paper, we focus on a corpus-based analysis of 1,043 social media items to determine the patterns of the students' vocabulary usage. By participating in activities over a year, the students gradually developed their propensity to proactively and spontaneously make meaning through interacting with their living spaces. This resulted in the retrieval of a greater diversity of the learnt vocabulary and the application of the language, particularly the use of significantly more "less frequent words" in the informal physical contexts, as compared to those from the formal or online contexts. While such findings affirm the notions of situated learning, authentic learning and contextualised language learning, we stretch the theoretical explication by connecting it with the students' intentionality in learning, with the "joint mediation" of the contextual affordances (the sources of inspiration for meaning making), social media network (providing students the sense of "communication with a purpose") and their handhelds (the tool for artefact creation and a reminder of their involvements in MyCLOUD) to sustain their activity level and therefore the cumulative development of their linguistic competencies.