Unfortunately the search API is fairly different from the rest of the REST APIs. We are working on getting them unified, but you'll need to treat the responses differently.
Some search API responses will contain a populated "geo" object:
Others will contain a "location", pulled from the user's profile location info. Sometimes this has coordinates:
"location": "iPhone: 40.643913,-73.749466",
but other times it may be arbitrary:
"location": "YYZ - JFK",
If you want to limit search results to those with either of these, use the geocode parameter and set the radius to encompass the Earth.