German is not mandatory for job seeking. You can apply for some positions in English (some job postings are even in English) and you can also get a work visa for highly skilled migrant without demonstrating German knowledge. But I am not aware of any “job seeker” visa (except for people who just graduated from a German higher education institution), you will need to get a concrete job offer before applying for a visa.
In practice, some companies do hire English-speakers but not knowing German will dramatically reduce the pool of potential employers. Unless, you have some very specific skills/experience that might convince a large, internationally-active company like SAP or IBM to hire you, I don't think you would have much chance on the German job market.