Understanding customers' opinion and subjectivity is regarded as an important task in various domains (e.g., marketing). Particularly, with many types of social media (e.g., Twitter and FaceBook), such opinions are propagated to other users and might make a significant influence on them. In this paper, we propose a fuzzy propagation modeling for opinion mining by sentiment analysis of online social networks. Thereby, a practical system, called TweetScope, has been implemented to efficiently collect and analyze all possible tweets from customers.