Fox is a furbearer species and therefore technically illegal to trsp without the proper permit and during the season. However, if it were my chickens at my house, i would set a "box" trap baited with sardines or tunafish. Once you catch him and possibly other would be predators (raccoons, skunks, opossum etc) call wildlife control for removal or relocate yourself. Live traps are indiscriminate and like a box of chocolates, you never know what you're going to get. Most wildlife officers understand this and will help you with a nuisance animal. But technically illegal so your call.
We have all sorts of predators from bear to bobcat that wander through the yard every night and have only ever lost 1 bird. That was in the middle of the day while chickens are free to roam the yard and woods. Night time safety has been achieved with an elevated coop, welded wire (no chicken wire) and latches on every point of entry. Our "adolescent" birds (up to 4 mos) are raised in a flight pen (8' x 30') that is welded wire to 7ft high with chicken wire ceiling. Base of fence is anchored by 6x6 timbers buried in the ground. Inside the flight pen they have an elevated coop with additional locks so even if fox gets in the pen they cant get in the coop.
If animal control won't help, and your uncomfortable addressing the situation yourself, beef up security with heavier wire and ground anchorage.
Photo shows the coop for free range adults on right and flight pen for adolescents on left