This is very difficult. Most of the records of Salvation Army Personnel were lost.
There is a website and a centre where you can go in London. They do charge quite highly for using their facilities.
The only way to trace people who worked for them is to search through individual copies of Warcry and it isn't indexed.
I have the same problem - trying to trace a Captain with them

Information here:-
http://www.rootschat.com/links/09e/ (click on Family History)
Some Officers' Career Cards (summary of appointments and promotions) have survived, but many, especially from the early years, have not. Many records were lost when the International and National Headquarters in London (101 Queen Victoria Street) were destroyed during the Second World War. When Career Cards have not survived, officers' appointments and promotions may be listed in The War Cry, or The Officer magazine. Don't know if local branches could help you
Tricia