iPhone that has bees lost for a few weeks

Assuming that you enabled the Find My option on the phone, it will not show up on a map if the battery has run down or it does not have an Internet connection at its current location.

Unfortunately, there is not much that you can do other than keep trying.

Apple does not get involved with lost or stolen iPhones, so no options there.

Apple does not track iPhones.

If you don’t see it in the find my app there is nothing you can do but file a police report, report it to your cellular carrier and buy a new phone.