how to make the random enemy generation with in the orthographic view of camera?

![alt text][1]

Hey i am making a game in which these red circles are enemies and the blue is player. player will move on accelerometer. now there are two things which is causing me problem. 1.)Enemy Ai problem: the enemies are following the player properly in unity editor when i porting the game in android device the enemies follow ai work weird enemies just slow down following and sometimes they stops.

1. Enemy Spawning: i want to spawn the enemies within the camera filed of view randomly from any where. [1]: /storage/temp/61120-demo.png