In this study, we investigate whether and to what extent community managers in online collaborative communities can stimulate community activities through their engagement. Using a novel data set of 22 large online idea crowdsourcing campaigns, we find that moderate but steady manager activities are adequate to enhance community participation. Moreover, we show that appreciation, motivation, and intellectual stimulation by community managers are positively associated with community participation but that the effectiveness of these communication strategies depends on the form of participation managers wish to encourage. Finally, the data reveal that community manager activities requiring more effort, such as media file uploads vs. simple written comments, have a stronger effect on community participation.