As I’m UK based here’s some UK contacts taken from the NHS webpage:

• Samaritans (08457 90 90 90) operates a 24-hour service available every day of the year. If you prefer to write down how you’re feeling, or if you’re worried about being overheard on the phone, you can email Samaritans at jo@samaritans.org.
• Childline (0800 1111) runs a helpline for children and young people in the UK. Calls are free and the number won’t show up on your phone bill.
• PAPYRUS (0800 068 41 41) is a voluntary organisation supporting teenagers and young adults who are feeling suicidal.
• Depression Alliance is a charity for people with depression. It doesn’t have a helpline, but offers a wide range of useful resources and links to other relevant information.
• Students Against Depression is a website for students who are depressed, have a low mood or are having suicidal thoughts.
• Bullying UK is a website for both children and adults affected by bullying.

Also: 

Get Connected for U-25s in the UK. Get Connected is an incredible organisation.

Further afield: 

Australia:

 Lifeline (lifeline.org.au) is a 24-hour nationwide service that provides access to crisis support, suicide prevention and mental health support services.

Canada and the USA: 

The National Suicide Prevention Lifeline (suicidepreventionlifeline.org) based in the United States is also available nationwide in Canada it is a 24-hour, toll-free, confidential suicide prevention hotline available to anyone in suicidal crisis or emotional distress.

New Zealand:

Lifeline Aotearoa (lifeline.org.nz) and Lifeline New Zealand (lifeline.co.nz) are New Zealand organisations providing free 24-hour counselling and phone help lines.