Citizen science continues to grow, potentially increasing competition among projects to recruit and retain volunteers interested in participating. Using web analytics, we examined the ability of a marketing campaign to broaden project awareness, while driving engagement and retention in an online, crowdsourced project. The campaign challenged audiences to support the classification of >9,000 pairs of images. The campaign was successful due to increased engagement, but it did not increase the time participants spent classifying images. Engagement over multiple days was significantly shorter during the campaign. We provide lessons learned to improve targeted recruitment and retention of participants in online projects.