Execution is actually not the main part of a startup. That's a common misconception. The main part is validating your idea; making sure that you're building the right thing. (What people often call product/market fit.)
There's actually a good bet that for only a little time and/or money, you can validate your idea, even without cofounders, employees, or friends who might be interested. There's a lot of ground to cover there, and since that's not what you were asking about directly, I'll spare you the details. But Steve Blank's course over on Udacity is a great introduction, as is Eric Ries's book The Lean Startup.
If you can get out the door and validate your idea, the investors, cofounders, and early employees may even come to you. Who could resist jumping in to a company where you talked to 100 people from the expected customer segment, 94 of them handed email addresses over to you, and 36 of which were basically telling you to shut up and take their money?
But as far as actually finding people goes, getting your friends to help is actually usually not that great of an idea. You don't want "friends" to help you, you want people with the right set of skills to help you. That's occasionally your friends, but probably not usually. And a lot of times, when you bring them along and they're not the right people, you ruin the friendship. So it's probably a good thing that you don't have friends who can help you.
As far as practical places where you can find people to help, you might want to consider going to a startup meetup group. Meetup.com was useful for me. It may or may not be for you. When you come into these types of events, you know all the people around you are at least interested in startups and the life that comes along with it. That's much of the battle with finding these people, and here, they've already self-selected into that.
Likewise, taking your idea to a startup "jam session" type event such as startupweekend.org helps a lot of people find others to help work on their idea.