Here's Tom Daley's contribution:
Actor and writer Mark Gatiss, star of The League of Gentleman, did a joint selfie with his husband, fellow actor Ian Hallard.
Radio 1 DJ Scott Mills has joined in.
Lots of trans guys have got involved too, like Switchboard patron Lewis Hancox, star of Channel 4's My Transsexual Summer.
And the artist, activist, and filmmaker Fox Fisher.
Trans campaigner and blogger Leng Montgomery said the Switchboard has "been invaluable in times of need".
YouTube star and LGBT advocate Calum McSwiggan has fronted the campaign posting selfies as well as a series of YouTube videos.
Switchboard wants to reach out to as many young LGBT people as possible, so lots of teenagers have joined in with the hashtag selfies, like this guy.
And this blogger.
This 16-year-old too.
And this guy.
These women too...
The selfies are being taken in all kinds of locations. This guy was outside the Waldorf hotel.
This student was in the library having a break from studying.
This woman was in France.
And this woman was in Austria.
People from every walk of life have been joining in. Like this photographer.
This musician used his French Horn rather than his hand.
This man was in his leathers when he tweeted his selfie.
And this Switchboard patron was by the Thames.
The helpline was set up in 1974, since when it has been helping LGBT people deal with a huge range of issues, providing emotional and sometimes practical support around coming out, HIV/AIDS, discrimination, bullying, mental health problems, and hate crimes.
Each year 15,000 people use the helpline and associated online services. The London Lesbian and Gay Switchboard hopes that by promoting what it does on social media, more LGBT people will ask for help when they need it most.