Might this be Hybrids by David Thorpe?
It was published in 2007 (smack dab in the middle of the period you suggested), the plot matches your description (judging by this review), and the cover has someone with what appears to be a computer screen for a face, with a smiley face emoji on it:
In an increasingly authoritarian Britain, not too far into the future, a new and dreaded virus is sweeping the country. Creep radically alters DNA and once infected, sufferers risk becoming merged with any item of technology that they over-use. It's a terrible disease, causing terrible pain and infection at the transition point and sending the body's immune system into overdrive. People are not only disabled by Creep; they are dying from it too. Nobody knows where Creep came from, but many suspect a drug company may have developed the disease in order to profit from curing it, but it mutated so quickly they were left with a disaster on their hands instead.
Britain's economy has collapsed and other countries are forcing it into isolation, afraid the disease will spread. Unsurprising, then, that those who suffer from Creep - known as hybrids - are feared and reviled by the general population and increasingly regulated by the authorities and the dreaded Gene Police and their Centre for Genetic Rehabilitation. Hybrids follows two Creep victims, Johnny Online and Kestrella, as they try to find out what is really going on.
David Thorpe's Hybrids won a recent new children's author competition run by Saga Magazine and Harper Collins. I can see why it was chosen - there were lots and lots of things I enjoyed about it. It's a real page-turner and my sons and I - even my younger son, the notorious reluctant reader - fairly galloped through it in our rush to find out what happened at the end. The narrative is told turn and turn about by Johnny and Kestrella and while I don't usually like a book to have multiple narrators, I enjoyed it here. It gave a double perspective on the disease and it also made the love affair between the two much more accessible to pre-adolescent readers.
It also tackles a lot of big themes - overdependence on technology; bad behaviour on the part of big business; family loyalty and, above all, mob reaction and public panic. My older son said, perceptive as ever, that he had thought Hybrids was going to be "just another" book all about how we should be nice to someone that's different, but it wasn't really about that at all - it much more about how "the people in charge" fail to control mob rule and actually "pretty much suck up to it really". And do you know, I think he was right. We also liked the way the book ended on more questions, not neat solutions.
Our one real criticism of Hybrids is that Creep is just too, well, crude. The subtlety of the themes and ideas in the book simply isn't matched in a virus that causes specific people to merge with specific items of technology that they over-use. We just didn't believe that a mobile phone would suddenly jump up and meld to Kestrella's hand. Or that a computer monitor would take the place of Johnny's face. Or that arms could become automatic machine guns. A more subtle virus causing a more subtle hybridisation would have improved the book considerably for us. Other than that, we really enjoyed Hybrids and hope it does well.
