Kate McCann, whose daughter Madeleine was abducted in Portugal in 2007, says she has not been put off competing in the London marathon by the Boston bombings.
She is an ambassador of the Missing People charity and is aiming to raise £20,000 to mark its 20th anniversary.
"This sickening act is just incomprehensible and the loss of life, especially that of a young child, heart-breaking.
"But I feel strongly that you can't live in fear or you don't have a life."
More top news
Police investigating the murder of Akhtar Javeed have arrested a second man in Leicester on suspicion of murder.
Nottingham’s tram network is reminding customers of some temporary changes to services on the city centre section.
A major inquiry has been launched in to the suspected abduction of a woman who is thought to have been forced in to a car against her will.