Google Scholar can help you find articles and books.   If you're comfortable searching Google, this may be a good place to start.   

You may want to read this Frequently Asked Question on how to get the most out of Google Scholar

Encyclopedia of Social Work: 

A continuously updated online collaboration between the National Association of Social Workers (NASW Press) and Oxford University Press (OUP). Building off the classic reference work, , it includes articles on key topics ranging from international issues to ethical standards. New articles and revisions to existing articles added regularly.

Encyclopedia of Women Social Reformers

NASW: Social Work Pioneers Biographies

• Biographical information about "social workers who have explored new territories and built outposts for human services on many frontiers."

Social Work Hall of Distinction

• Biographical information about social workers from California.

Notable American Women

• Notable American Women is an online book that gives biographical information about historical American Women. The first installment went from 1607-1950. You can look for your reformer or pioneer by last name in the index:
  • v. 1 A-F   v. 2 G-O  v. 3 P-Z 
• The next installment covers the rest of the twentieth century:
  • Notable American Women: Completing the Twentieth Century
• Another installment covers the Modern Period:
  • Notable American Women: The Modern Period

Social Welfare History Project

• The Social Welfare History Web site is a nonprofit project designed with the goal of better informing the public about the history of American social welfare. The link will take you to the part of the site which has biographical information. See below for other useful info on this site.

Includes:

• Chronology of events from 16oo's to 1999
• Programs  developed by topic such as Adoption, Child Labor, Settlement Houses, etc
• Biographical entries
• Eras: Slavery, Widows & waifs,Civil Rights, etc.
• Organizations and Recollections and Opinions

Women and Social Movements in the United States, 1600-2000

In addition to offering the Notable American Women books above this site includes primary source material. After searching for the person look for results under Author.

Trying using some of the following words combined with the name of your pioneer or a related subject.

*You may want to combine some of the above words using "or"