I started a Cosgrove Surname Project hosted at Family Tree DNA. It is open to anyone that carries the Cosgrove surname (or one of its variants such as Cosgrave and Cosgriff) and to those persons who have a Cosgrove family line in their tree.
FTDNA requires a DNA test to join their website. If you have already taken an automosal DNA test (such as AncestryDNA), you can transfer your results over to FTDNA for a small fee ($39 as of May 2016). If you haven't taken a DNA test, it is highly encouraged for males who carry the Cosgrove surname to take a Y-DNA test. Y-DNA testing is helping us establish genetic connections across the various Cosgrove lines.
The link to the surname project is as follows: https://www.familytreedna.com/groups/cosgrove-surname-project/