The words that you are looking for are:
「～～に」 and
「～～によって」
I would, however, need to remind you that the reason for describing an event (or situation) using the passive voice is often the very fact that the personal agent is of little to no importance to the speaker and/or listener.
This, coupled with the fact that both subjects and objects are often not mentioned in Japanese in the first place, can make your sentence sound unnatural if you inserted a 「～～に」 or 「～～によって」.
With that in mind, one could say:
「[私]{わたし}はアリスにどんな[動物]{どうぶつ}に[例]{たと}えられるの？」, which sounds more natural than
your own 「私はどんな動物にアリスに例えられるの？」, but both are correct.
Both mean "What kind of animal would I be compared to by Alice?"
Moving on to the money story...
To express who gave the money to Tanaka in the sentence:
「お[金]{かね}は[田中]{たなか}に[渡]{わた}された。」,
you can insert "by someone" right after お金は.
「お金はスミスによって田中に渡された。」= "The money was given to Tanaka by Smith."
In this case, it would be better using 「によって」 because a 「スミスに田中に」 would sound kind of clumsy with the "name に name に" structure.
As long as one avoids using the "name に name に" structure, one could use either 「に」 or 「によって」 to express a personal agent. When mentioning the personal agent is important or crucial, one would definitely choose 「によって」 over a plain 「に」.
