If you set up the Find My iPad service in the Settings prior to the iPad going missing, then there is a chance that can be tracked, wiped of its data or locked (which does the same thing as activating the screen lock), though it depends on a number of factors: the iPad is turned on, is connected to a WiFi or 3G network, and has not had the Find My iPad service turned off or the iPad completely restored. Log into icloud.com and go to the Find My iPhone section. If you did not set up Find My iPad, then there is no way to track it or lock it. Report the loss the police and change any passwords for any online accounts you may have used from your iPad (the iTunes Store, for instance).
As to your apps and music, you can see what content you can download here:
If you are eligible for re-downloading your content, see:
Forum Tip: Since you're new here, you've probably not discovered the Search feature available on every Communities page, but next time, it might save you time (and everyone else from having to answer the same question multiple times) if you search a couple of ways for a topic, both in the relevant forums and in the Apple Knowledge Base, before you post a question.
Apple (and no one else) can not assist (with serial number or iCloud) in finding a lost or stolen iPad.
Report to police along with serial number. Change all your passwords.
These links may be helpful.
How to Track and Report Stolen iPad
Reporting a lost or stolen Apple product
What to do if your iOS device is lost or stolen
iCloud: Locate your device on a map
Report Stolen iPad Tips and iPad Theft Prevention
How to recover a lost or stolen iPad
How to Find a Stolen iPad
What NOT to do if your iPhone or iPad is lost or stolen
Apple Product Lost or Stolen
Oops! iForgot My New iPad On the Plane; Now What?
If you don't know your lost/stolen iPad's serial number, use the instructions below. The S/N is also on the iPad's box.
How to Find Your iPad Serial Number
iOS: How to find the serial number, IMEI, MEID, CDN, and ICCID number