Describe your teacup in Google images and search online sales and auction sites. When you describe your piece, mention the pattern. Is the motif floral, geometric, is it transferware, or handpainted? Mention the primary colors used in the design as well as any other significant details. The cup may show gold edging or decoration. If so, state that in your description.
If the cup is floral, mention the type of flower. Notice if the flowers (roses are popular) are large or small. Other details may include leaves and vines. Also, notice if the design is inside the cup. If the design includes animals or birds, mention that.
What is the cup made of? Learn how to distinguish between porcelain and bone china. That will help in your search.
Change the description as you go if you can't find an image of your piece. Check back every few days as inventories change quickly. This may take some time, but with patience, you should find a similar piece pictured online.