Forums are discussion boards on the Internet. They can be used as well scaling customer service and to get feedback on a service or a product.
Copy support emails to the forums. Consider creating a forum thread for each support email you solve. Then the answer stays on the web so people can Google it.
Get new users hooked fast. Most forum users are one-timers that register, login, post and never come back. You must get them engaged on that moment. Send them a reminder after a week or so that their post have answers.
Design a solid forum structure. Create a logical structure for your forums so people can easily figure out where they should be posting. Especially important for newcomers that are a new to forums.
Use sticky threads. Use sticky threads to notify about the forum etiquette.
Always sort thread by popularity. Then threads that related to more people stay on the top and keep people engaged.