We find evidence of selective exposure to confirmatory information among 300,000 users on the investor social network StockTwits. Self-described bulls are 5 times more likely to follow a user with a bullish view of the same stock than self-described bears. This tendency exists even among professional investors and is strongest for investors who trade on their beliefs. Selective exposure generates differences in the newsfeeds of bulls and bears: over a 50-day period, a bull will see 70 more bullish messages and 15 fewer bearish messages than a bear over the same period. Moreover, beliefs formed in these “echo-chambers” are associated with lower expost returns. Finally, we show that selective exposure creates “information silos” in which the diversity of received signals is high across users’ newsfeeds but is low within users’ newsfeeds and that this siloing of information is positively related to trading volume.