This combo made from undated photos provided by the FBI shows cousins Elizabeth Collins, 8, and Lyric Cook, 10, right, who have been missing since Friday, July 13, 2012. (AP Photo/FBI)

EVANSDALE, Iowa --- Authorities hope a separate reward will help them locate two cousins who have been missing since July.

Elizabeth Collins and Lyric Cook-Morrissey disappeared four months ago while riding their bicycles in Evansdale. The case is being treated as an abduction.

Their families, in conjunction with Cedar Valley Crime Stoppers, are collecting donations now through Dec. 19. The total will be announced Dec. 21.

Anyone who provides a tip leading to the girls is eligible to receive the money. Currently, a $50,000 reward has been offered for an arrest and conviction.

“There is someone out there other than the person or persons responsible who knows something that could help these families out,” said Brice Lippert with the Waterloo Police Department and Crime Stoppers, speaking during a press conference Monday at the Evansdale Police Department.

Elizabeth’s dad, Drew Collins, said a good friend heard about a similar reward being offered in a Des Moines case. He and his wife, Heather, suggested the idea to Lippert.

“Someone has to know something,” he said.

Evansdale Police Chief Kent Smock thanked the public for keeping the girls in the forefront and stressed the importance of spreading the word.

“We continue to make it known that we’re still looking for that one last clue that will get us where we need to go,” he said.

Donors can mail tax-deductible contributions to Crime Stoppers c/o Elizabeth and Lyric Fund, P.O. Box 1510, Waterloo, IA 50704, or drop off donations at the Evansdale, Cedar Falls or Waterloo police departments or Black Hawk County Sheriff’s Office.

Contact the Crime Stoppers to request a receipt.

There will be no door-to-door solicitations related to the fundraiser, according to organizers.