No - even the GC doesn't do it. It doesn't find all references to any
particular object, it just finds all objects which have live
references.

Profilers can do this, however. Unfortunately I don't have any
particular recommendations in terms of profilers.

As Jon pointed out there is no builtin mechanism for this; code inspection
might help here. One thing that can unintentionally cause references to
remain live are subscriptions to events that are never unsubscribed as the
event itself holds a reference to the subscriber. Other things to look at
are static fields that hold references to objects.

I'd run your app under a memory profiler and look at what's on the managed
heap. There are several free ones; I don't have links but it should be easy
enough to google some up.