First you must decide if there are or aren't or if you can see two sides to this issue.
If you believe there are and have evidences to prove that, your statement should read something like this:
Angels do indeed live among us as evidenced by (reason 1), (reason 2), and (reason 3).
Another type of thesis statement might look at the idea first you are not trying to prove and then end with that idea you are proving. For example:
Although many claim this idea of angels among us entirely true, research demonstrates this is simply impossible.
A final method if you plan to look at both sides might be this:
The debate about the existence of angels provides heated and valid arguments on both sides.
Hope that helps.