A subject database will almost always cover more journals and cover different dates in your field than does Web of Science (WoS), so it will often be possible to find additional citations. In addition, one simply can't rely on the completeness of coverage in Google Scholar.
Note: Many databases have only fairly recently begun to track citations.
The following databases provide cited reference searching:
Alt-Press Watch - Proquest Search Tips
Communication Abstracts - Proquest Search Tips
Communication & Mass Media Complete - EBSCO Search Tips
Criminal Justice Abstracts - EBSCO Search Tips
Criminal Justice Periodicals - Proquest Search Tips
ERIC - EBSCO Search Tips
JSTOR - JSTOR Search Tips
Political Science Abstracts (Worldwide) - Proquest Search Tips
ProQuest Central - Proquest Search Tips
Includes the following databases:
ABI/INFORM
Accounting & Tax Periodicals
Banking Information Source
Career and technical education
Criminal Justice Periodicals
Dissertations and Theses
Education
Psychology
Research Library
Social Sciences
PsycINFO - Ovid Search Tips
Social Services Abstracts - Proquest Search Tips
Sociological Abstracts - Proquest Search Tips
Worldwide Political Science Abstracts - Proquest Search Tips