Hi Ashok,
Unfortunately as far as I know :contains CSS selector is not supported by TestComplete currently.
If you have stable html text but no stable attributes, you can use either:
1) var link = NativeWebObject.FindChild('innerHtml', 'Log Out', 1000)
You'll have to map some object that will be a parent for 'Log Out' link in object browser.
or
2) var link = page.FindChildByXPath("//a[text()='Log Out']);
You have to declare what is page before you use 2.
for example:
var page = Sys.Browser("*").Page("*");
Hope it helps.