Tl;dt; The simplest way to connect users to one another in an online community is to keep an eye on users’ interests and needs that can complement each other.
When you see users who have some needs on one hand and other users who have an interest in meeting those needs on the other hand, and the users do not intersect naturally or intersect but not in a timely manner, you need to help coordinate the users. The easiest approach is to maintain relationships with active regular users and know the types of activities they prefer to act on. When these activities appear on the platform, notify the users so they can show off their skills. This can be done manually by you, by volunteers, or via some automatization if your platform supports it.
This is a fragment of a draft of the book “Lessons Learned While Working On Stack Overflow”. Read the full book on kindle or the paperback version.