The easiest way to resize a VHD file is via command line. Check this blog post on technet.com.

Note: maybe you googled for VHD Resizer (or vhdresizer) and could not find the download.

If you need VHDResizer, check this blog post on burksy.net (it contains a working download link).

Note: I used BitLocker to password protect my virtual disk. After executing "extend" I had no feedback. This because I forgot to unlock my drive. After unlocking it I could extend the partition as wished.