Welcome.

A companion voucher is for BA metal only. From the USA you can only fly to London and onwards if you want to use a companion voucher.

Your main problem will be finding availability from LAX/SFO-LHR. You can add an onwards BA flight, eg Europe, Africa, Asia, etc.

Otherwise, you can redeem avios on OW partners (AA, CX, LAN, etc) or other BA partners.

http://www.flyertalk.com/forum/briti...tart-here.html
http://www.flyertalk.com/forum/briti...vios-beta.html