How can I find open physics postdoc positions in Europe?
Many jobs are only advertised on the website of the respective universities. Often professors post positions on their home pages or group pages, so it may be a good idea to keep an eye on them. Sometimes job openings are also mailed around to colleagues, so it is a good idea to let people know you're on the market, so they can forward these announcements.

Depending on your particular subfield there may be other relevant websites as well.