Currently, it is not possible to use the tracking number field to global search for sales order and / or item fulfilment associated to the tracking number. This is covered by Enhancement 132192 - Global Search>Search transactions by tracking number field.
As an alternate solution, you can create a transaction sublist view with tracking number as available filter using the following steps:
1. Navigate to Transactions > Sales > Enter Sales Order > List
2. Make sure that View=Default
3. Click on Customize View button
4. On the Available Filters tab, set the following:
a. Type and Show in Footer=T
b. Tracking Number and Show in Footer=T
5. On the Results tab, expose the following fields [but is not limited to]:
f. Tracking Numbers
6. Assign a name on the Search Title field
7. Click Save
Once the result is generated, you may change the value on Type field to Item Fulfillment if you wish to pull up item fulfilments based on the entered tracking number in the Tracking Number footer filter field.