In order to create a segment based on a specific product, please follow this instruction:
Step 1: Go to Customers tab >> Manage Segment >> Create new segment
Step 2: Create a segment of customers who bought a specific product in your store. Kindly choose "Have performed event", attribute "Order Success" >> tick With data >> event Product >> Add the specific products to the list box
Beside the event Product, you can freely choose among: product collection, product name and product tag. Moreover, the With frequency option can be chosen if you want to add an advanced rule: Customer has bought it n times.