Having an intuitive developer portal is only the beginning of building your API community. Both online and offline aspects can really help you engage with the developers who use your API. The same methods can also help you identify or attract potential developers. These are all pretty much must-haves, but be sure to share in the comments the ones that you think are most important.
1. Encourage (and answer) questions in a forum
Creating a forum for questions about your API might not be mind-blowing advice. However, the key is to also actively use the forum: encouraging developers to ask their questions publicly, so that the answers eventually help the greater community. Don't look at the forum as support—this is community-building. By taking it public, developers can even lend a hand and help their fellow developers. Facebook went beyond a forum and took their developer advocates where the users are—in this case, with a special Stack Overflow forum in which questions are tagged 'facebook.' Not only does Facebook carefully watch Stack Overflow, but the social network also actively markets it as a destination for questions.
2. Blog frequently
If you want to be a Resource for developers, you need to continually help them see the possibilities: sharing example apps and techniques, shining a spotlight on top developers, and highlighting other kinds of knowledge on your company blog. If developers aren't the core audience of your company, creating a separate tech blog might make sense, but make sure that you have enough content. However, developers don't want to wade through numerous nontechnical posts for the material written to them, so keep a balance.
3. Get your social on
Go where your developers are. At the very least, they're likely on Twitter, so make sure you're actively participating in discussions there. Like using the blog, having separate Twitter accounts for separate purposes might make sense. If your core audience isn't developers, you want an API-specific account—as Twitter does, naturally. Some providers even choose to have a specific account for status information, giving developers more granular control over the types of messages they receive (and implicitly, how those messages are received). Other social networks might be useful, depending on your audience. See how top social APIs use social media.
4. Put your face forward
Developers should be able to put a face--or faces--to the company. Knowing that you're there for them is one thing--on forums, via blogs, and on social media--but knowing who is there is another. You should have one or more people in the company focused on your API community. Even if that person performs another job, make sure developers know that he or she is available. Put names, photos, and e-mail addresses in highly visible places, like the forum, in the bylines of blog posts, and on the Developer Portal.
5. Show off developers in an app gallery
A well-rounded community encompasses a lot more than just you. Create an app gallery, and shine a spotlight on your best developers. Write blog posts that highlight new, notable, or promising projects. Regardless of what you think about the current state of Flickr, Yahoo's photo-sharing Platform does a good job of showing off its developers.
6. Attend and organize events
Most of your API community interactions take place online, but providing opportunities to meet in person can build stronger bonds. For example, attend hackathons and help developers create something new in a short time. Just remember the key to developer marketing—share knowledge, not features. You want to help developers so that they think of you and your API when they build the next thing. If you simply sell to them, they'll remember that, too, but probably not in a good way. In addition to attending hackathons, consider workshops, meetups, happy hours, or even full-fledged conferences. The choice is going to depend on your audience and your ability to staff whatever event you attend or organize. Which of these six ways to engage your API community is your favorite? Which one did I miss? Adam DuVander is Developer Communications Director for SendGrid and Contributing Editor at ProgrammableWeb. Previously, he edited this site and wrote for Wired. You can follow him on Twitter.