Hi and Welcome. My Name is ***** ***** I look forward to assisting you today with your question.
What version of Mac OS X are you using ?
You don't need any app for that. Open Safari. Then go to www.icloud.com
Login to your iCloud account. This will bring iCloud website. Click Find iPhone button.
This will show all your Apple devices on the map. Now click on All Device on the top middle and select iPhone. You can do the iCloud operations from there.
If you have any difficulty, please let me know and I will continue to help you.
Here is the direct link to Find iPhone --> http://www.icloud.com/find
Refer this article --> https://support.apple.com/kb/PH2698?locale=en_US
If you have any questions or would like continued help, please reply back to me here and I will continue to help you
Do you still need help ?