Cook County Sheriff Tom Dart said Monday about 70 families whose loved ones went missing in the 1970s have contacted the department.
Dart says the families described loved ones who fit the description of Gacy's known victims. Gacy is known to have killed 33 young, white males who lived and worked in the Chicago area between 1972 and late 1978.
Two Chicago-area families already have provided DNA samples and another family is set to be tested. DNA kits also have been mailed to Minnesota and Iowa authorities.
Dart says it will be weeks before authorities get the DNA comparisons back.