Tonetti and O'Donohoe have signed up for another two years, while Gannon and Moore have penned one-year extensions.
The players' commitment has come as a timely boost ahead of Connacht's interprovincial clash with Munster this Saturday in Galway and for head coach Eric Elwood the pieces of the jigsaw continue to fall into place as he puts his squad together for next season.
Speaking about the signings, Elwood said: "Competition for the scrum half jersey has been fierce this season and that has brought out the best in the players, so it's great to have Paul and Dave Moore, along with Frank Murphy, competing in that position.
"Kyle has been outstanding for us in the centre in both attack and defence and Dave Gannon provides us with a range of options in the forwards.
"He has really shown his versatility playing in both the second row and back row, so we're delighted to have him on board as well."
Paul and Kyle both played for Elwood's Ireland Under-20 Grand Slam-winning side in 2007 and have been ever present in the province's squad this season.
Known for his hard-running lines and blistering turn of pace, the powerful centre is as comfortable playing 12 or 13 and has won a number of in-house plaudits, including the Player of the Month award, for his exceptional work-rate across the pitch.
Arriving last summer from Leinster, the 24-year-old O'Donohoe was capped 16 times in the league and twice in the Heineken Cup by his native province before hooking up with his former underage coach Elwood again.
Alongside winning the Leinster League Cup with Clontarf, the lightning quick number 9 has been a highly consistent performer for Connacht this season.
Speaking about his deal, Tonetti said: "I'm delighted to commit to Connacht, the province is going from strength to strength and it is an exciting place to be at the moment.
"I'm happy to concentrate on the rugby now and having that bit of security is great. The work Eric and the management team are doing at the moment will mean we have a more settled side next season and I'm delighted to be a part of that."
O'Donohoe added: "I'm really happy to be staying at Connacht, it's been great to get the opportunity of regular game-time here and I will keep pushing for that starting spot.
"The next two years are going to be very exciting for Connacht Rugby and it's great to know I'll be involved for them."