I've started to use google to verify term paper authenticity. I'm
entering the title and/or the first line of the paper. Are there more
efficient methods?

Hello and thank you for your question.

I wouldn't assume that the cheater will copy the title of the paper
that he or she copies.  So you'll do best to choose some key words
from the text itself.

And loyal as I am to Google, I must say I have had better results in
tracking down plagiarism with a different search engine,
www.alltheweb.com

I used alltheweb.com in catching the (apparent) cheater in a question
I recently answered for another customer here:
http://www.answers.google.com/answers/threadview?id=340915

In addition, you should be aware that there are commercial services
that will check proprietary databases for a fee:
http://www.plagiarism.org
http://www.turnitin.com 

Search terms used:
I searched answers.google.com for my prior answers, and for the names
of the commerical cites

Thank you again for bringing us your question.  I hope you find my answer useful.

Sincerely,
Google Answers Researcher
Richard-ga

Your method sounds like a good way to catch the most blatant
plagarism.  My view is that entering random lines from the paper will
enable you to check for more sneaky plagarism, hiding somewhere in the
text.  In addition to selecting a few random lines, you could find
lines or phrases that don't sound typical for a student.

Checking random lines may catch students who copy long passages from a
web page indexed on Google.  Checking atypical lines or phrases may
also catch students who copy smaller portions.

One more comment: I suppose the method will depend on how many papers
you have to check.  Entering four or five lines per paper on Google
might be efficient enough if there are only twenty papers to check. 
But I imagine that you wouldn't be so happy to do that if there are
fifty papers.  In that case, I would suggest checking two or three
atypical sounding phrases, or if you detect none, checking a couple of
phrases at random.

Thanks, I'll also try alltheweb.

Go to turnitin.com 

All colleges use this to submit papers for this reason. Trust me it is
great. They will mark all your parts that it picks up through a major
scan of universities and libraries.