ANSWER: Interest groups are group of persons, who has come together as a legal body to achieve one goal, and speak the mind of each member as a group. Example of these groups are: American society of home inspectors, American land title association, International code council, and many more.
This groups keeps the public informed about important issues, by the use of it's official pages and using media stations to inform the public.
For example: An interest group called "AIDS policy center for children, youth, and families" can keep the public informed about a special issue, by visiting a media station to buy time and inform the public at that time, or advertising their information at the media stations and news papers.