I believe there have been a few threats already regarding this subject. But since that is an answer worth nothing:
"When circling to land on a different runway, the pilot has to carry out the published missed approach for the original runway not the runway he circled towards."
I suppose you will find this info also stated in your OM-A, chapter 8.
Look at it this way: for example, you are on the instrument approach for runway 18, but circling to land on runway 36. It is not necessary that runway 36 has a published missed approach procedure. Maybe there is only an ILS on runway 18, and no instrument approach at all for runway 36.
With that in mind, the missed approach to be flown is the published missed approach from the "original instrument approach" flown, thus runway 18.
As of how to fly the missed approach, it depends on your position.
Either you are still on the instrument approach. You just continue straight and follow the procedure as you would do on any normal instrument approach.
If you have left the instrument approach and begun the circling part of the approach, you will turn toward the airport, climb MSA, turn in the circling area towards the published missed approach.
Also, this info is written in your OM-B.
Goodluck
