Amber Heard, Tina Knowles Lead Effort for Habitat for Humanity

Hollywood's rallying behind Habitat for Humanity L.A. ... with Amber Heard, Tina Knowles and Lance Bass leading the way to raise some good money for a great cause.

Amber, Tina and Lance are just some of the many celebs who are helping the org raise awareness and funds through a social media campaign dubbed #Hammertime. The funds will help build homes during the COVID-19 pandemic for families in the Hollywood community who can't afford it. Some of the dough will also be used as valuable resources for families in need.

Scores of other celebs, including Tori Spelling and Holly Robinson Peete, have signed up to help launch the social campaign. For every $25 or more donated to HFH L.A., donors can get a special steel hammer created by Redline Steel ... a veteran-owned, American-made hammer perfect for hammering away while building a new home.

Jo-An Turman, VP of entertainment partnerships at Habitat L.A., tells TMZ ... "these beautiful gifts will help the org continue to build hope, homes and address the need for affordable housing."