Conference papers are included in the same online databases that also include journal articles, however, the most useful databases to search for conference papers are:
ACM Digital Library provides access to the full-text of articles from journals and conference proceedings published by the ACM (Association for Computing Machinery). This includes the SIGGRAPH series.
The IEEE/IET Electronic Library (IEL) contains almost one-third of the world’s current literature in electrical engineering, communications, and computer science. Search over 3 million full-text documents
GDC Vault is a collection of in-depth design, technical and inspirational talks and slides from the influencers of the game development industry, taken from over 20 years of the worldwide Game Developers Conferences.