Surveying Land - Mysterious Plot of Land

[Joseph Aceves]

Behind the property I manage is one residential house and a parking lot for a restaurant. And between the two, still behind the property I manage, there is a mysterious square of land. It seems like it would have made sense to be connected to the residential house, but the fence for the house doesn't include it in, leading me to believe it is owned by someone else. 

How do I go about finding who owns this property most efficiently? Would hiring a surveyor be the best option? Any and all feedback or advice is much appreciated.

All the best, Joe