A private organization plans to search an area in Stoneham this weekend and excavate an area in Woburn next month, in hopes of finding evidence that will solve the mysterious October 1989 disappearance of Woburn high school freshman Melanie Melanson.

The Woburn police will observe and are prepared to assist, while Middlesex prosecutors “support any efforts made in finding Melanie,” said Stephanie Guyotte, a Middlesex district attorney’s spokeswoman.