I lost my iphone 4s last week can anyone help me to get it back????

Only if you installed "Find my iPhone" prior to the loss, you could be able to log into iCloud and track your device. If you did not install and activate your account in iCloud, there is no other way to find your phone.

iCloud: Troubleshooting the Find My iPhone app

iCloud: Troubleshooting Find My iPhone, iPad, iPod touch, or Mac

Sorry, then there's no way to locate the iPhone.

Regards.