Search engines are defined in the file core/DataFiles/SearchEngines.php

Each search engine is defined by a new line with the following format:

"" => array( "Search engine name", "keyword parameter", [optional path containing the keyword], [optional charset used by the search engine])

For example, for Yahoo!

""      => array("Yahoo!", "p", "search?p={k}"),

The macro {k} will be automatically replaced by the keyword to link to the search engine page for the keywords found in your Piwik reports. The main search engine URL has to be at the top of the list for the given search Engine.
Note that some search engines can have several variable names to define the keyword, you can specify an array of names. For example, for the search engine, the keyword can be found in “wd”, “word”, or “kw”, and the keywords are encoded in the charset “gb2312″. The line for looks like:

""         => array("Baidu", array("wd","word","kw"), "s?wd={k}", "gb2312"),

When adding a search engine, please also submit the search engine icon, for the directory plugins/Referers/images/

Please submit to the Piwik team the new search engine line in SearchEngines.php and the icon; we will add it for the next release!