To search comprehensively, it will be necessary to use multiple sources. Bibliographic databases provide the best functionality for performing and saving a structured search. There is some overlap between the databases in terms of the journals that they index but each one also has unique content and therefore it is essential to search more than one. For information on which databases to search you should consult a relevant library subject guide.
It may be necessary to search supplementary sources where it is unlikely that all of the required information will be indexed in a bibliographic database. This may involve citation searching, journal hand searching and searching for information that has not been commercially published which is also known as grey literature. This type of searching should be documented in your protocol and the final search strategy and methods section of the review.
JBI has produced a short video with some really useful tips.