Two-tone necklace with heart pendant — sentimental gift

I lost my two-tone gold-and-silver necklace yesterday around 3pm near the Peace Gardens by the Winter Garden in Sheffield city centre. It's about 18 inches long, with a delicate heart pendant that holds a tiny cubic zirconia stone and has a small initial 'P' engraved on the back. The brand is Pandora, and the chain shows a little patina but is otherwise intact. It was a gift from my grandmother, so it means a lot to me and I’d really love to get it back.