In the 1930s, Placzek was known as an adventurous person with sharp sense of humor, a tireless generator of novel physics ideas which he generously shared with his colleagues. The scope of Placzek's pilgrimage around the world's physics centres in the 1930s was unique among his colleagues. He worked with Hans Bethe, Edward Teller, Rudolf Peierls, Werner Heisenberg, Victor Weisskopf, Enrico Fermi, Niels Bohr, Lev Landau, Edoardo Amaldi, Emilio Segrè, Otto Frisch, Leon van Hove, and many other prominent physicists of his time. His wife, Els Placzek (née Andriesse) was an ex-wife of physicist Hans von Halban. He lost all his relatives to Holocaust, casting a tragic shadow on his life.