Social trading platforms are an increasingly popular venue for sharing investment ideas. We investigate if followers on these platforms herd, i.e., copy leader traders’ trades, to the extent that it affects stock markets. To do so, we use an event study to detect abnormal returns and trading volume after a trade is conducted by a leader trader. Furthermore, we investigate if the leader trader’s sentiment on the stock and the leader trader’s perceived trustworthiness have explanatory power over the herding behavior. We find signs of herding in terms of abnormal returns within thirty-minutes after the leader trader’s trade. However, we do not find signs of herding for longer event windows, nor do we find that the sentiment of the leader trader can explain herding. Finally, we find some signs that affect-based signals of trustworthiness can explain herding. However, most signals of trustworthiness are non-significant.