I can confirm the same issue, in "Ubuntu" 14.04. In 13.10 Dolphin "Find" work flawlessly, however since upgrading to "Trusty" "Find" returns no results at all.
It appears this is a problem which may not be resolved until KDE 4.14. Note the latter part from the following extract:
"....A major new improvement is the introduction of KDE’s next generation Semantic Search. This makes search faster, saves memory, improves stability, and generates more reliable search results. And it could use a good testing.
Various applications use the search abilities, most notably Dolphin and KDE PIM (see the next section). Also tagging (Gwenview!) and KRunner (Alt-F2 run command dialog) can use some attention.
Some of your existing data will need to be migrated from the current Nepomuk backend to the new 'Baloo' backend. Running the nepomukbaloomigrator should take care of that. The old Nepomuk support is considered “legacy” (but it is still provided). The programs that have not yet been ported to the new architecture have Nepomuk integration disabled. One significant regression is file-activity linking, which will not work until KDE Applications and Platform 4.14. If you rely on this feature, we recommend not upgrading at this time. For the final release, distributions might choose to optionally have the old search (Nepomuk) available. ...."
..."
Above extract taken from: http://dot.kde.org/2014/03/12/applications-413-coming-soon-help-us-test