Location based Q&A

I am developing a location-based Q&A app. The main screen of the app features a map with a search box above it. When the user chooses a location, the "ask" button at the bottom is enabled and the user can move to the next screen for typing the question.

Mock

^{download bmml source – Wireframes created with Balsamiq Mockups}

Actual screenshot

How to make the map obviously clickable

There are two ways to pin a location in my app:

• Searching a location in the text box and choosing one from the autocomplete list. Users figured this out instantly.
• Clicking on a location on the map, and then the location name appears in the search box above.

I have tested the app with a few users, and the second option is not natural for them – they try to figure out a textual address rather than clicking on the map to figure out a location.

How do I make the map obviously clickable? Which text, icon or UX flow would make the users understand that they can just pin a location with a finger without searching for it textually?

Updates

There are a few great suggestions regarding the text field that I am going to seriously consider. I'd love to know if there are some ideas about any visual/graphic element that would help with hinting.