The present study examines the effect of conventional hashtags \& cashtags at social networks on the stock returns of S\&P500 companies. In the first step, by creating an optimization portfolio that consists of S\&P 500 companies (Fundamental analysis) abnormal stock returns have been tested. (similar to the 1989 study, Jane A. OU and Stephen H. Penman). Then, in the second step of the research, the effect of reduction free float of companies on abnormal stock returns has been tested. Next, the reduction of the explanatory power of EPS and BV information content as representatives of financial statements (income statement and balance sheet) on stock returns has been tested, and finally, in the fourth step, the effect of conventional hashtags \& cashtags in social networks at the site Stocktwits.com has been tested. The findings of this research showed that: although Jane A. OU and Stephen H. Penman 1989 rejected the hypothesis of a semi-strong efficient market in the companies surveyed, at this study and of course in the S \& P500 companies, the hypothesis of a semi-strong efficient market was confirmed. The effect of declining free float has led to abnormal returns on the S \& P500 companies. The explanatory power of EPS and BV information content on stock returns have diminished over time, which has been due to the hashtags \& cashtags content of financial statements on social networks. In other words, news about the status of companies is rapidly affecting stock returns through virtual networks.