Using the number of citations
Examples of expert searches in a database and a search engine that include bibliometric data :
Using the number of publications
By finding authors with high numbers of articles on your topic. This is usually possible by using the refining options of bibliographic databases.
Knowledge communities help you find collaborators, competitors, and potential partners.
Academic or professional social networks for researchers also help identify experts in a certain field. For information on networking, consult the guide Promoting Your Research Activities.
Here are some examples of such social networks: