I found a 2008 article that said Peter Schiff's classmate donated a photo of him that Peter had given him when they were both 12 years old. The article concludes that Schiff had died in the Holocaust with certainty, but Peter van Pels (Anne gave the van Pels family the pseudonym Van Daan in her diary, so he was called "Peter Van Daan" in her diary) was who lived in the Secret Annex with Anne, not Peter Schiff. Peter Van Daan's fate is known because Anne Frank's father witnessed it, so do articles and google image search show Schiff's photo as Van Daan's? Are Peter Schiff and Peter Van Daan two different people?
Peter Schiff was someone who Anne met at school and was indeed a different person from Peter van Pels. They were both Jewish, about three years older than Anne, and had the name Peter, but that was where the similarities ended. I have always wondered since people were given pseudonyms in Anne's diary why the two Peters were never differentiated with different first names.
Anne mentions seeing Peter Schiff in her diary a few times before she went into hiding, though Peter van Pels was not mentioned until after the Franks arrived in the secret annex. When Anne talks in her diary about "Petel", it is Peter Schiff she is referring to and not Peter van Pels. She had hoped that Peter van Pels could be a replacement of sorts for Peter Schiff.
Funnily enough, the two Peters and Hello (Anne's boyfriend before she went into hiding) were all three years older than she was, the same age as her sister Margot.
Also, Otto Frank did not exactly see himself what happened to Peter van Pels. The last time Otto Frank saw Peter alive was in January 1945 in Auschwitz, but Peter did not die until May 1945, on what became known as a death march between concentration camps. Peter Schiff, as far as I can tell, did in fact die in Auschwitz, though no one knows for sure when or where he died. All that is known is that he did die in a concentration camp.