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
Dry for much of the day with possible brighter spells in the east. Outbreaks of rain will spread southwards later in the day.
Another rather cloudy and mild day. Although dry for most the odd spot of drizzle is possible, mainly over high ground.
D-Day veterans from the West Midlands were given France's highest honour today, 18 months after a pledge to award every living soldier.