One of the most effective ways I know to increase student engagement is to reach out to students on a regular basis.  This can be emails, chats, group discussions, etc.  

There is no doubt that one of the single most important elements in student success, is the ability to interact with the instructor.  With some thought and creativity, this can absolutely be achieved in an asynchronous environment.

Having been involved with face to face, synchronous, and asynchronous courses, the material presented so far is very much on point.  There are certainly challenges that you face in the asynchronous environment, but it is satisfying knowing that you are working with students that may have no other way to engage in learning.