Sorry to hear that, Shannon! Hopefully Timo's suggestion works for you. If not, sadly you may need to buy another phone :( However not everything is lost, since nobody can access your own prepaid online account.
You'd need to buy a new SIM card and activate that on your account. Not only does that preserve your number, but the person who stole your phone won't be able to use up your minutes and data (hopefully they haven't yet).