Using novel data from a stock forum, we analyze return extrapolation in the cross-section. Our findings indicate that extrapolators overreact to the returns but underreact to the fundamentals. The post-earnings-announcement drift (PEAD) is more pronounced among firms with a high firm-level degree-of-extrapolation (DOX). Additionally, investors ask fewer questions about high-DOX firms’ fundamental information on official online interactive platforms. Extrapolation reduces the informativeness of stocks due to investors’ inattention to fundamentals. Furthermore, extrapolators’ overreaction to returns and underreaction to fundamentals increase stock price crash risks. These findings support explanations of extrapolation based on limited asymmetric attention.