If you have not noticed this yet here on myancestry.com they have a new file you can search for Irish relatives. I found advertisements for 2 different Irish relatives that have had significant and new information. Often the ads listed the county, town and parish the individual was born plus where the relative was who placed the ad was living.
These files are similar but much more complete to what was found in this Information Wanted collection from Boston College: http://infowanted.bc.edu/results/
Searching for Missing Friends: Irish Immigrant Advertisements Placed in “The Boston Pilot 1831–1920"http://search.ancestry.com/search/DB.aspx?dbid=5060
Even if you can't find your relative, you might be able to use the information you find on the surname - to rule out some individuals you might not be sure were relatives.