Both attackers featured in Saturday's friendly against Olympiakos.
Speaking after the 1-1 draw, De Rossi said: “The more we go on, the more new faces I can see.
“We need that great passion around the players. Some have been sold, others forgotten, but the fans must cheer everyone on because they gave so much to this team.
“Everyone plays their part in convincing players. The director and CEO Lina Souloukou work with the figures, I talk to the players. Every coach in the world talks to the prospective players, otherwise transfers don’t get done.
“In the situation with Dovbyk, Dan Friedkin was fundamental and we are all happy and grateful about that. We needed a player like this, he’s a very interesting prospect and will need time, but has settled in pretty quickly already.
“The great thing is that all the players who arrived really wanted Roma, even giving up on extra money and more prestigious clubs on paper.”