Hi Azita.Raissi,
Thanks for visiting Apple Support Communities.
If you're using a PC, see these articles for help with using Find my iPhone via iCloud.com:
iCloud: Find My iPhone overview
http://support.apple.com/kb/PH2696
iCloud: Troubleshooting Find My iPhone, iPad, iPod touch, or Mac
http://support.apple.com/kb/TS4006
Best Regards,
Jeremy