The phrase "amassing a team" is correct and usable in written English.
You can use it when referring to the act of gathering or assembling a group of people for a specific purpose or project.
Example: "The project manager is amassing a team of experts to tackle the new initiative."
Alternatives: "building a team" or "gathering a team".
The actor plays Colonel Stars and Stripes, a gun-toting patriot amassing a team of superheroes, but recently U-turned on the film, tweeting that he was not ashamed of it but, in the wake of the Sandy Hook shooting, was withdrawing support due to its "level of violence".
Teraltyics has raised around $44 million to date, telling TechCrunch it's taken investment up to a Series C level, and amassing a team of 65 people working out of headquarters in Zurich and offices in New York and Singapore.
All told, the trustee has amassed a team of more than 200 to unwind the firm, in addition to the roughly 200 MF Global employees who were retained.
PEER 1 has a team of 5 people based in NYC, but with the help of friends, partners and customers (like the CEO of Squarespace) who chipped in after seeing what PEER 1 was doing to keep things up and running, they amassed a team of about 35 people, including Mike Mazzei, the head manager in NYC.
Nearly every Wednesday (sometimes there are Internet reruns), a new episode of "Zombie College" pops up on the powerhouse animation site www.icebox.com, which has amassed a team of producers and writers associated with television programs like "The Simpsons," "King of the Hill," "Seinfeld" and "X-Files".
Founded at Stanford in 2011 by Duplan when he was just 19, Clinkle amassed a team of smart, driven students at the college despite refusing to show many a working prototype.
Kushner, whose venture fund Thrive Capital has $200 million under management with bets in Instagram, Nasty Gal and Warby Parker, has amassed a team to revolutionize health insurance through a new stealth startup called Oscar.
The player must amass a team of rockers to help recover this guitar and defeat the monster (called "The Beast").
The No. 1-seeded Orange amassed a team-record 34 victories, with Boeheim passing John Wooden for N.C.A.A. tournament victories.
Receiver Michael Thomas led the NFL with 125 catches, including 12 against the Rams in Week 9. Thomas amassed a team-record 211 yards receiving and sealed the victory with a 72-yard touchdown catch.
Experience is heralded as the most important trait when it comes to amassing a strong team.
