I'm running an up-to-date debian testing with kde plasma version 5.13.2, kernel 4.16.0-2 on an hp laptop. Whenever I enter anything into the "type to search" field of the Application Launcher, plasma immediately crashes. I tried reinstalling kde-plasma-desktop but the behavior persists. So the search function in the application launcher is completely unusable. This seems to be similar to the issue reported in Bug ID 391613 and 382970 I'm not attaching a backtrace because the bug reporting window said the information would probably not be useful.
It is very likely to be Bug 391613 or Bug 382970, but without a backtrace, it's impossible to tell. I'm not aware of any Plasma developers who experience this issue, so there's sadly not much we can do with this bug report. You might try installing debug symbols and reproducing the crash again. Your distro may have up-to-date documentation on how to do that. Until then, I have to close this bug If you manage to produce a useful backtrace, please attach it and re-open the bug. Thanks!