Online reviews are a dominant resource for consumer. Extant research on online review generation has primarily focused on the valence of online review, the volume of online review however remains largely unexamined. This study examines the peer effect on content production. Using a unique data set, we track and measure peer effect at message level. We find that peer effect does exist and it is attributed to the characteristics of the receiver, the object and the message, the relationship between the sender and the receiver. Intriguingly, our findings show that not all friends have the same effect on content production. A user is more likely affected by friends who share salient and relevant content and whom the user admires. Our findings hold implications for online review platform designer and marketers in terms of utilizing peer effect to facilitate content generation and spreading Word of Mouth.