What is the best way of finding someone you lost track of in the USA?

Finding their cell phone number and calling them?

I think it's people find or something online, you can google find people and use the sites to search and gather as much free info as you can. Look up names of relitives of the person b/c older people don't move as much. Call them and tell them you are looking for someone you lost touch with. If it's the wrong number, try the other numbers. Also try searching facebook and myspace for their name and names of people you remember might know them or heard where they are now. You can also hire a private detective. They find people all the time.

Phone # (old or new) location, such as area code, zip code. Name: First, mid, last. How you knew them, did you know them from a certain town, job etc. Use the info you have and try to expand on it. All you can do. P.S. Make sure they want you or would not mind you finding them. Dont be that weirdo!

Google their name or go to zabasearch.com and see if you can find them there.

By google, type:
phone directories
you have, whitepages, zabasearch, infobel, intellius, etc... many stuff like that, but be careful if they ask for credit card numbers or any other personal information. I don't give any info personally.

Begin by googling every variation of their name that you can think of. I recently found a friend I'd lost touch with over 25 years ago by searching through google. And don't lose heart...my friend was clear into the 20 something page of similar names....your friend may not be easy to find but it will be worth it when you do re connect.