Yes you can Search!
If you're visiting from the website:
Click on the magnifying glass icon at the top of Tophatter, and enter some keywords describing what you're looking for.
From the app:
Tap Browse, then tap the magnifying glass icon in the upper right.
Some items are available to Buy Now, or you can tap the heart icon to set a reminder for items so you don't miss them when they open for bids.