New suitors are circling 21st Century Fox Inc., affirming that the media empire built by Rupert Murdoch is now in play.

Comcast Corp. has approached the media company to express interest in buying a substantial piece of it, according to people familiar with the situation. Verizon Communications Inc. is also kicking the tires on Fox assets, though a person familiar with its thinking cautioned the exploration was in the early stages. And Sony Corp.’s entertainment unit has also informally approached Fox, the people familiar...