The Glasgow firm said its new studio gives it capacity to more than treble staff numbers from the current 12.
It is recruiting designers, programmers, character artists and producers to work on the online multiplayer role-playing game Celtic Heroes, and will take employees at the firm to around 20.
Alex Wozniak, community manager at One Thumb Mobile, said: "The new premises on Mitchell Lane are around three times as big and give us the space to have things like meeting rooms.
"We are looking to expand how many people we have and there is a wide range of roles we are looking to fill.
"We think that will take us up to about 20 and that would put us at a good size to keep our players interested and develop new things for them to do."
The game, launched in June 2011, allows players from around the world to go on quests and battle with enemies, but is currently only available on Apple devices such as the iPad and iPhone.
One Thumb Mobile is taking on the extra staff to increase the platforms upon which Celtic Heroes can run, including devices with Android software.
That should lead to a rapid increase in the user base, which currently stands at 630,000 registered accounts.
The company also plans to continue to develop the micro-transactions, which allow players to spend real money, starting at 69 pence, to upgrade their in-game capabilities and buy special items.
Mr Wozniak added: "Hopefully with the expansion [of the game] we have coming out over the next few weeks we will see an increase in the number of registered users.
"We have released three significant updates, and we release patches so we can introduce new content to provide new things for players without them having to download the app each time.
"[Android] means we can get on to more devices and reach a wider global market. We want to expand the game, bring new players in and let more people experience it."
Mr Wozniak confirmed One Thumb Mobile is concentrating its resources on Celtic Heroes and was not yet developing other titles.
He said: "We want to make [Celtic Heroes] as good as we can before we start thinking about anything else."