What are the best design principles to foster participation and engagement with an online solution?

This is a very vague question, so it's hard to answer. However, I don't think it's enough to design the experience.

For example, you will need to make sure that your potential customers:

• know about your solution in the first place
• are convinced that it provides more benefits than the competitors' solutions
• are convinced that it's a less risky choice than other solutions (e.g. if you are just starting out, potential customers may be concerned about you going out of business, which may not be an issue for your established competitors)

I believe it's mostly about marketing and not the product. Even if your product is a lot better than the competition, if nobody knows about it, it won't go anywhere.

This should not have been voted down, its a legitimate question. The way I would approach it is to do a design analysis on your top competitors. Fixing their design flaws in your own product can be very smart.

Unfortunately there is not a specific design pattern I can point you to. What i would suggest is to highly focus on the user experience in two areas:

1. Simplicity, making the application easy to learn, and easy to use.

2. Wow factor. For a web app you can create the wow factor with a little bit of Jquery or other Javascript code. Bandwidth has increased a lot to be able to handle this, and it really makes your app stand out.

If I understand the question here are a few people and resources that may help:

• Check out Stephen P. Anderson, his Mental Note cards are focused on applying psychological principles to web design.

• Susan M. Weinschenk's book Neuro Web Design is excellent, she has a great blog on the topic as well.

• For a look at the darker side see Brian Meidell's document What I Learned From FarmVille - So You Don’t Have To Play It, which explores how Zynga uses compulsion and social pressure to keep its players addicted.