Welcome to Android Central! Which device do you have? Tap the menu button (the 3 vertical dot button onscreen, or the physical Menu button if your phone has one), then tap Search. Do you not see that?
I just switched from a Galaxy S3 mini to an S5 mini. I was a very happy user of Google Sky Map on the S3 mini and earlier Samsung Android phones. Now I no longer have a menu button at the top of Sky Map, or anywhere else that I can see. I am hoping Sky Map chooses the location from the GPS/Location readings as I now have no way of entering a location manually. And I cannot search. I hope someone reading this either has the answer or can persuade the relevant folk at Google to update the app to cope with the change in menu location