After a participant has engaged on one of your projects it is important to showcase a list of other engagements that might be of interested to them. This is where you can make use of the acknowledgement message, found in the tool settings, configured and updated regularly, to alert participants to other interesting engagements.
For example, in the survey settings you can configure your acknowledgment message as illustrated below with pictures and links of interest to your participants.
Once the participant completes the survey he would see the acknowledgement and a gentle reminder of other interesting things to do on the site.
A good message can encourage participants to share their contribution with their networks, friends and family, which will increase the participation and promote the consultation.
The similar acknowledgement option is present for the other tools like Quick Poll, Stories, Guestbook, and Q&A. The Idea and Forum tools provide the "Share" button for instant sharing and promotion on social media and via email.