Verizon’s $4.4 billion bid for AOL has put the spotlight back on public tech company valuations. But more startups are joining the ranks of “unicorns”, or private tech firms that have been valued at $1 billion or more. A recent study by KPMG and CB Insights estimates that 50 firms could attain unicorn status in 2015, with 14 already signed up in the year to mid-April.