If you have sent your invitations via the AwesomeBox site, we'll send reminders to your invitees via email. Reminders are sent two days after the first invitation is sent, and again two days prior to the deadline for participating.
An host can also send a reminder at any time, which is important if your box's deadline is longer than one week from the day you started it.
Click on the gear icon in the section at the top of the AwesomeBox group page. Click the "Send Message" button, and you can enter a custom message to be sent to anyone who hasn't participated yet.