The way I was approached as a marketing co-founder is that I reconnected with a friend at our high school reunion. He was a highly technical founder who had run his business for a year but wasn't getting the results he wanted. He had no marketing expertise and offered me a majority equity share to come on board. It took me about a month of deliberation before I accepted, but I decided to accept because:

1) he demonstrated he was flexible and willing to change the business model based on my advice
2) he clearly showed that he valued my skills by offering such a high equity stake and
3) our existing relationship (we were very good friends all through middle and high school) put me at ease. I already knew his personality and liked working with him.

Don't underestimate the value of personal relationships. My networking strategy has always been to start with my existing network of people and ask them to introduce me to two new people. The strength of a personal referral is much stronger than bumping into someone at an event and your contact can often be a great source of research for you before you meet with your new contact.