One of the quickest ways to find the closest relatives of someone who has passed away is to find their obituary, because the obituary almost always tells the surviving spouse, children, siblings, and often nieces, nephews. So if you can't find the relatives via Intelius, try to find the relatives via one or more obituaries.
1. Google the person's name in quotes, plus the word "obituary" or with the phrase "born in"
2. Ancestry.com; (charges) Sear the word "obituary" to get the following results
US Obituary Collection, 1930-2015, 34.6 million names;
Obituary Times Index, 1995-Present, 16 + million names
National Obituary Archive (NOA), with 55 million + names
Canadian Obituary Collection, 1898-2015, 1.2 million names;
Social Security Death Index, 1935-2014
3. Check FamilyTree.com
4. Search NewspaperArchives.com
5. Check obituary databases that have been established:
6. FindaGrave.com, 152 million grave records
7. Legacy.com, millions of obituaries
8. Tributes.com
Reference Books that tell obituary sources:
1. The Source: A Guidebook of American Genealogy, ed by Arlene Eakle and John Cerny, 1997. (I think this is that big red book.)
2. Check recent genealogy reference books in WorldCat;
3. Google "finding obituaries/an obituary" , "how to find obituaries/an obituary"