Originally answered Jan 23, 2018
The 90–9–1 Rule of Thumb suggests that only 10% of the group members will contribute at all, and only 1% will regularly do so. 90% will not contribute at all.
Getting other people to participate in wikis is a challenge. Wikis are often created by a committed individual who hopes that others will share a similar passion for the topic and add to the content. When these others fail to materialize, the wiki ends up being maintained primarily by the original creator, and thus is more similar to a blog or website.
If the main purpose of the wiki is to collaboratively edit a document or list, then try the strategies in How to motivate knowledge sharing using gamification, goals, recognition, and rewards. However, be prepared for them not to work.
If the main purpose is something else, try using an Enterprise Social Network (ESN) or a Team Space instead. The rule of thumb still applies, but you have a better chance of people posting, replying, or uploading files than you have of them editing or creating a wiki page.