Gold-plated chain necklace with initials pendant

I lost my gold-plated chain necklace yesterday around 3pm outside the Bullring, near the Selfridges entrance on Corporation Street in Birmingham. It's an 18-inch slim chain from Moon & Co., with a tiny heart pendant that has the initials 'A.J.' engraved on the back. The chain is slightly worn and there’s a small scratch on the pendant and a faint rainbow sheen along one link. It’s sentimental to me—my grandmother gave it to me, and I’d really appreciate getting it back.