The PDF is fully searchable. Simply use the search functionality of you PDF viewer or the hyperlinked index at the end or, like me, both (e.g. go to the start of the index using the PDF bookmarks and start to search there after the macro you are looking for).
There is http://www.texample.net/tikz/, especially http://www.texample.net/tikz/examples/tag/manual/
which has many of the examples of the TikZ manual and other LaTeX examples, but I don't think there is a full HTML version of the manual. Converting all the pictures to images, or even SVG, wouldn't be efficient.
While Google and other search engines provide HTML versions of PDFs in general, the TikZ/PGF manual "
pgfmanual" is to large for that. AFAIK the maximum size for this online service is 1MB or so.