This paper aims to identify and model relationships between cryptocurrencies market price changes and topic discussion occurrences on social media. The considered cryptocurrencies are the two highest in value at the moment, Bitcoin and Ethereum. At the same time, topics were realized through a classification of the comments gained from the Reddit social media platform, implementing a Hawkes model. The results highlight that it is possible to identify some interactions among the considered features, and it appears that some topics are indicative of certain types of price movements. Specifically, the discussions concerning issues about government, trading and Ethereum cryptocurrency as an exchange currency, appear to affect Bitcoin and Ethereum prices negatively. The discussions of investment appear to be indicative of price rises, while the discussions related to new decentralized realities and technological applications is indicative of price falls.
