You do not need the Find My iPhone app. Go to www.icloud.com, sign in with your Apple ID and track. Now, if you mean that you did not activate Find My iPhone in icloud and you didn't, then there is nothing you can do.
What To Do If Your iDevice Is Lost Or Stolen
If you activated Find My Phone before it was lost or stolen, you can track it only if Wi-Fi is enabled on the device. What you cannot do is track your device using a serial number or other identifying number. You cannot expect Apple or anyone else to find your device for you. You cannot recover your loss unless you insure your device for such loss. It is not covered by your warranty.
If your iPhone, iPod, iPod Touch, or iPad is lost or stolen what do you do? There are things you should have done in advance - before you lost it or it was stolen - and some things to do after the fact. Here are some suggestions:
This link, Re: Help! I misplaced / lost my iPhone 5 today morning in delta Chelsea hotel downtown an I am not able to track it. Please help!, has some good advice regarding your options when your iDevice is lost or stolen.
It pays to be proactive by following the advice on using Find My Phone before you lose your device:
2. Setup your iDevice on iCloud
If the iphone was "stolen" that means that theres is a person who intends to keep it from you. If that is the true intent, then your ability to "track" was likely disengaged within the first five seconds by powering it off. Use iCloud to protect your data by placing a lock code on your iPhone or erasing it entirely. Tracking down the thief is a matter best left to law enforcement agencies.