Another option, if people are finding it tough to get users to donate, is to ask users to complete an action that will support the site. For example, you could ask users to take a short survey to support your site. Users who might not usually give monetary donations would have another option to help support. Survata has a good option for this (note: I do work there) and we're always looking for new publishers to add to our network. Feel free to reach out to    [email protected] for more info.