Open Jaw booking
 

I typically use Google flights to search flights and then book from the linked website. But I can't' figure out a way to look up an open jaw trip.
I'm traveling from San Francisco to London, and then either Rome or Naples back to San Francisco.
Could someone point me to a good tool to search for this?
When I search for 1 way tickets between these destinations, the added cost is very high ($4k +).

Google Flights facilitates open jaw searches. Click the Round trip dropdown right above the departure airport field, and you will see One way and Multi-city. Click Multi-city.

https://cimg7.ibsrv.net/gimg/www.fly...12573c3400.jpg
Click where it says Round trip.


https://cimg3.ibsrv.net/gimg/www.fly...877d3ffc84.jpg
Click Multi-city.

Multi city search