Demi Lovato has tweeted her support to her best friend Selena Gomez.

The 'Neon Lights' singer posted a heartfelt message on Twitter yesterday (05.02.14) after news broke that Selena spent two weeks in rehab this January, with TMZ claiming she was treated for alcohol, marijuana and prescription drug Ambien dependencies.

The 21-year-old star wrote: ''Weakness is living in denial. Only the strongest people ask for help.''

Demi famously checked into a treatment facility in December 2010 for help with an eating disorder, self-harm and depression, only revealing last winter that she also had serious drug and alcohol dependency issues at the time.

Selena is said to have sought help to work on her ''emotional life'' because of her on/off relationship with wild child Justin Bieber.

A source told E! News: ''The last straw was seeing them on the Segways. She needed to work on her emotional life. She needed to learn tools on how to deal with Justin and letting go of that relationship.

''This is the first time she's ever taken the time to deal with issues, to deal with herself, with a therapist.''

A representative for the 'Come & Get It' hitmaker confirmed Selena had spent a fortnight at Arizona's Dawn at the Meadows last month, but denied she had ''substance abuse'' problems.

Selena and Demi - who first met as children on the set of 'Barney & Friends' - recently rekindled their friendship, with Selena admitting she felt guilty for not supporting Demi during her darkest hour because she didn't understand what she was going through.