As far as I know, they have to serve the warrant on the person who controls the property to be searched. In this case, that was Google.
"Two Out Of Three Cases Where Google Gives User Data To Government Don't Involve A Warrant
1/23/2013 @ 12:10PM
It may be easier than you think for government entities to demand the private data you’ve stored on Google’s servers. Most of the time, it doesn’t even require a judge’s signature. On Wednesday Google released its semi-annual Transparency Report, its voluntary admission of how many times it removed data from its services or quietly handed users’ information to government agencies in the last six months. Between July and December of 2012, Google says it received 8,438 U.S. government requests for its users’ data and complied to some degree in 88% of those cases. That’s up a remarkable 33% from the 6,321 data requests Google received in the same period the year before, and marks a 70% increase since Google first started issuing its Transparency Reports in 2009. But the new wrinkle in Google’s data is a breakdown of how many of those requests approached Google with a search warrant: Just 22%, according to the company. By contrast, 68% of requests were issued only with a subpoena, which unlike warrants don’t require showing a judge “probable cause”–solid evidence that the data was relevant to a crime. (The other 10% of the requests involved some sort of court order or other miscellaneous process.)"