You maybe have flashed the MIUI rom custom on your device. HTC or not, but there is no play Store and you can't live without that.
If you don't know MIUI, you can:
- read my article: Official MIUI.us v4 Review
- watch my video: YouTube
This is the How To install Gapps - Play Store on your MIUI device.
1 - Download the last Gapps here:
Goo.im - Gapps
Miui.us - Gapps
If it doesn't work, try to find it on Google by gapps download + your device name.
2 - Put it on your device.
3- Flash it with the recovery like the rom custom (but without any wipe)
4- Restart your phone & Enjoy